There were 63 players who started at least half of their teams' games at offensive tackle during the 2015 NFL season (Detroit had a right tackle-by-committee situation). Only nine of those tackles had joined their respective teams as undrafted free agent signings.

READ: FREE AGENCY FOCUS - DEFENSIVE END

Of those nine players, only two played the critical left tackle position: Branden Albert in Miami and Jared Veldheer in Arizona. Veldheer is the great archeological find of the bunch, that long-sought leg bone that proves the existence of a species. The species of which we speak is the starting left tackle who hits unrestricted free agency after his rookie contract and signs with a new team. Albert, in contrast, was able to hit the market after six years in Kansas City when the Chiefs drafted his replacement (Eric Fisher) first overall and tried unsuccessfully to trade him. He had previously been retained in K.C. via the franchise tag.

The Oakland Raiders drafted Veldheer in the third round and, over the next four years, watched him develop into one of the league's better left tackles. In 2014, the Raiders chose not to use the franchise tag on their starting blindside protector and he quickly signed with the Arizona Cardinals, whose head coach was shocked that Veldheer was available. Veldheer has since started all 32 games for a Cardinals team that has gone 24-8, made two playoff berths and fielded the league's top-ranked offense in 2015.

The point is, free agency is not the place to find a starting left tackle, not because it's a bad idea (though it proved to be one for the Bucs and Anthony Collins in 2014) but because it's rarely possible. Signing a right tackle is a slightly more attainable goal, as there were seven 2015 starters who joined their current teams as unrestricted free agents. Those seven were almost all players who had left their previous team in search of a better starting opportunity. Jermey Parnell, for instance, started only seven games in four years in Dallas before signing with Jacksonville last year. Marshall Newhouse started seven games with two different teams in 2013-14 before getting a shot to play right tackle for the Giants last year. Jason Fox made three starts in three years in Detroit, signed with Miami in 2014 and didn't become a full-time starter until last year.

READ: FREE AGENCY FOCUS - WIDE RECEIVERS

Of course, if one expands the definition a little bit beyond unrestricted free agents, the examples become a bit more plentiful. The Buccaneers got very good work last year out of Gosder Cherilus, who they signed in August to replace the injured Demar Dotson. Cherilus was only available because he had been released by the Colts. The Buccaneers released long-time left tackle starter Donald Penn after the 2013 season and he has since gone on to start the last two years in Oakland.

Now Penn is an unrestricted free agent, part of what is a typically thin group of available veterans at the tackle position. The Buccaneers, who essentially have three starting tackles on their roster, including one they drafted with the 34th overall pick last year, would not appear to be the first shoppers in line when the tackle market opens next Wednesday. Donovan Smith, last year's high-second round pick, impressed the team with his play at left tackle as a rookie, and both Dotson and Cherilus remain under contract. Still, at the right price, Tampa Bay would have to at least consider an addition to the position, if only for depth and competition.

READ: FREE AGENCY FOCUS - TIGHT ENDS

In the weeks leading up to the start of free agency on March 9, Buccaneers.com is taking a position-by-position look at the players who may be available when the market opens, hoping to determine the ones who could be good fits for the Buccaneers. The usual caveat applies: This is not meant to reflect the opinions or strategies of Tampa Bay General Manager Jason Licht, Head Coach Dirk Koetter or any of their assistants. In fact, since the players mentioned below are still under contract until the start of the new league year, Licht and company could not comment on them specifically even if they wished to do so, lest they be guilty of tampering.

So, after previously checking out what the market has to offer at defensive end, wide receiver, guards/centers, linebacker, running backs, defensive tackles and tight ends, we now turn our attention to…

Offensive Tackles

Lo and behold, there's another leg bone in this year's dig: Seattle's Russell Okung. Okung, the sixth-overall pick in 2010, is hitting free agency after his initial deal, though in his case it was a six-year contract. He has been the Seahawks' starting left tackle for that entire run, but he has also missed 24 games due to injury over that span, including three last year. Okung has yet to play a full 16-game season in his NFL career. That certainly will factor into a team's evaluation of his value as a free agent, but Okung is a proven starting tackle and that will surely find him another multi-year contract somewhere, if not back in Seattle.

READ: FREE AGENCY FOCUS - DEFENSIVE TACKLES

Cordy Glenn was a second-round pick by the Bills four years ago but he represents that class of blockers that rarely makes it to free agency. Since he has developed into one of the league's best at his position, Buffalo didn't hesitate to slap the franchise tag on him before the start of this year's free agency period. On the other hand, the Browns did not choose to put their tag on Mitchell Schwartz, perhaps because he plays right tackle instead of left. Cleveland should be expected to push hard to bring Schwartz back, however, after he has started all 64 games since being selected 37th overall in 2012. If Schwartz does depart, he would represent a very nice addition for his new team.

The same would be true of Baltimore's Kelechi Osemele, who was picked 23 spots after Schwartz in that 2012 draft. Some consider Osemele the best available offensive lineman this year, after the tagging of Glenn, but the question is what position he'll play under his next contract. Osemele has spent the majority of his four years with the Ravens at left guard, but is also considered capable of excelling on the edge. He started his whole rookie season at right tackle and last year filled in some at left tackle. He is likely to be one of the most coveted players on the entire market if the Ravens don't re-sign him before next Wednesday.

READ: FREE AGENCY FOCUS - GUARDS AND CENTERS

There are a handful of veteran starters, a little longer in the tooth, who will have a chance to sign new deals this spring, including the aforementioned Donald Penn. Penn is 33 and has started 140 games over the last nine years, but his improved play over the last two years in Oakland won't go unnoticed if he fails to re-sign with the Raiders. Andre Smith has been holding down the right tackle position for most of the last five years in Cincinnati, is not yet 30 and was part of a very good Bengals front last year. That said, Cincy drafted not one but two tackles in the first 53 picks last year (Cedric Ogbuehi and Jake Fisher) and still have standout left tackle Andrew Whitworth under contract for one more year. That could make it very difficult for the Bengals to retain Smith if he seeks his true market value. If he departs, Smith should step right in as a starter on the right side for his new team and provide an instant upgrade.

The timing of his first shot at free agency is both good and bad for Pittsburgh's Kelvin Beachum. On one hand, he has used the last four years to develop from a seventh-round pick into an above-average left tackle starter, and he could be seen as one of the biggest "upside" signings of the tackle group this spring. On the other hand, he missed the last 10 games of the 2015 season after tearing an ACL, so the state of his recovery from that injury will play a part in team's evaluation of him. San Diego's Joe Barksdale, on the other hand, started all 16 games last year and played reasonably well on a battered Chargers front. He's bounced around a bit in five years – Oakland to St. Louis to San Diego – and may not be considered the same sort of upside play, but he has no injury issue and should have no trouble attracting interest on the market.

READ: FREE AGENCY FOCUS - LINEBACKERS

The timing is good for Atlanta's Ryan Schraeder, in a way, but it's also good for the Falcons. Schraeder has risen gradually from an undrafted free agent in 2013 to a full-time starter in 2015, and he's coming off a very strong season. However, with just three years under his belt, he will be a restricted free agent this year, which makes it highly likely that the Falcons will retain his services for at least one more year. If he plays on the one-year RFA tender offer, however, and continues his ascendance, Schraeder will have a chance to cash in next year at this time.

Thirty-year-old Ryan Harris has started for three different teams in the last three years, most recently with the Super Bowl champs after returning to Denver last year when the Broncos ran into offseason injury troubles on the line. Harris had not been asked back by Houston or Kansas City the previous two years but obviously showed he could be a stop-gap last year in Denver. Former Saint Jermon Bushrod is not far removed from being a big-ticket UFA signing himself, but he gradually lost his job with the Chicago Bears so may be viewed as a depth signing at this point.

Will Beatty wasn't starting or playing last season, but it wasn't because he was beaten out for the Giants' left tackle job. Rather, he missed the season due to a pectoral injury and torn rotator cuff, and two weeks ago the Giants released him after a failed physical. That obviously makes him an interesting case in this year's free agency run; he has had some very good seasons but has also come up against eye, back and leg injuries over the last four seasons.

There are opportunities for teams to build depth. Bobby Massie and Byron Bell were both right tackle starters last year, in Arizona and Tennessee respectively, but are now free agents and may have to win a starting job anew this year. Chris Clark started 21 games for Denver in 2013-14, then got traded to Houston last summer and started just four games. He'll be looking for another shot at age 30. Chris Hairston bookended that Chargers line with Barksdale for part of the year, also playing both guard spots at some point. He's only 26 and also had 15 starts in Buffalo from 2011-12 so he'll probably get another shot through free agency to make a team in 2016.

Bucs' Overall Interest Level at the Position: Low

The Bucs have a promising young starter at left tackle in Smith and a potential battle at right tackle between Dotson and Cherilus. Dotson started the last three games of the 2015 season after coming back from his preseason knee injury. Offensive line depth does tend to turn over from season to season, so the Buccaneers will almost certainly be looking for some additions. However, they can just as easily address that issue in the draft, so they will probably not be in competition for the bigger names on the offensive tackle free agency list.