MOBILE, Ala. — So much about the Bucs remains a mystery, even as draft preparations start to ramp up with this week's Senior Bowl.The team has yet to hire a coach. Even when it does, it will remain unclear what type of defense it will employ until a staff is in place.But this much is unequivocal: The Bucs' defensive performance in 2011 can't be repeated if a turnaround is in the team's future.In their effort to improve their 30th-ranked defense, don't be surprised if Tampa Bay embarks on a search for more playmaking from its linebackers, a position that was under great scrutiny during the season.One possible source: April's draft, where some candidates will be available, including some participating in this week's senior showcase.The outside linebacker talent is likely to draw more attention from the Bucs. Mason Foster, though still raw, proved adequate at middle linebacker as a rookie this season. (It remains to be seen if a new staff keeps him there.) But weakside starter Geno Hayes struggled and could become an unrestricted free agent in March. Strongside starter Quincy Black is just one year into a five-year deal but also underperformed.Outside linebacker options being evaluated here this week include Nebraska's Lavonte David, North Carolina's Zach Brown, Texas' Keenan Robinson and Miami's Sean Spence.Brown has impressed onlookers, showcasing the speed he believes will set him apart from his peers."Brown can run like the wind," NFL Network analyst Charles Davis said after Tuesday's South team practice.But the former Tar Heel runs with one purpose: take down ballcarriers. He describes himself as a sure tackler. "As a tackler, I do whatever I have to do to get a guy on the ground," said Brown, 6 feet 1, 236 pounds. "I'm locked in when it comes to that. I had to remind myself out here (at practice). I had a chance to take out a running back, and I had to hold up a little. "But I don't miss a lot of tackles because I take a lot of pride in my tackling. I try to make sure that if you come my way, you're going down."Another projected 4-3 linebacker worth tracking is David. Considered undersized at 225 pounds while at Nebraska, he fits the mold of some Tampa Bay linebackers of the past.If a team can live with his lack of bulk, it will acquire a player whose production can't be questioned. Playing at a school with a legacy of producing defensive talent, David ranks fifth in school history with 274 tackles. Like Brown, David's speed is hard to miss. He also showed a knack for playmaking.For many years, that was a quality that characterized Bucs linebackers. But not last season. Spence, a high school teammate of David in Miami, believes he possesses the ability to make game-changing plays NFL teams expect from their linebackers."I think (scouts) will see that I'm a playmaker," Spence said. "I think I'm very instinctive, and I'm a guy who is going to play hard and sell out for the guys who are around me. I'm also a three-down linebacker."Spence played mostly on the weakside at Miami but has extensive experience in the middle and on the strongside. His size is an issue, too. The All-ACC pick measured just under 6 feet and 228 pounds but still managed to play physical football.This linebacker class doesn't include a player who seems worthy of the Bucs' No. 5 overall pick. But with high second- and third-round picks, Tampa Bay will get a chance to address the need. And given the results in 2011, there's little doubt the Bucs need the help. Stephen F. Holder can be reached at email@example.com. View his blog at tampabay.com/blogs/bucs and follow him on Twitter at @holderstep hen.