TAMPA — For an NFL defense trying to get off the field, third down can feel like everything. Make a stop, there's momentum. Fail to do so consistently, frustration sets in.Perhaps the biggest difference between the promise of last year's 9-7 Bucs and the disappointment of this year's 2-5 team is third down. Tampa Bay was the league's toughest third-down defense in 2016 and now ranks as the NFL's worst."You have to have the mentality that it's a takeaway if you get off the field," safety Chris Conte said. "It's a big play and something that as a defense we haven't executed very well."Cornerback Robert McClain's pick-six in the opener against the Bears came on third down. So did defensive end Noah Spence's sack-fumble that set up another touchdown.Since then, the Bucs have struggled on third down. Even in a solid game defensively Sunday against Carolina, the lone touchdown in the first three quarters came when the Panthers went 5-for-5 on third down. The compounding effect of third-down struggles can be psychological."I think it can be, when you get in a game and it seems like you can't get off" the field on defense, coach Dirk Koetter said. "I've seen games like that before on both sides, when you're converting every third down or you're not. I think that can get in your head a little bit, but I don't necessarily think that's the issue here."Part of a third-down problem is struggles on first and second down. Bucs opponents need an average of 6.75 yards on third down this season, the fourth-shortest average distance in the league.Third down might be where the Bucs' lack of a pass rush is most obvious. Third and long is an obvious passing down, allowing defensive linemen to focus on getting to the quarterback. The Bucs had 18 third-down sacks last year, sixth-most in the league; they have three this year, on pace for a league-low seven."It's definitely your mind-set," defensive tackle Gerald McCoy said. "You have to not take 'no' for an answer. Do whatever it takes to get off, because it's our job to not let them score but also get the offense the ball back. Winning third downs is like a turnover … at some point, players just have to make plays."Sunday's opponent, Saints quarterback Drew Brees, is not the kind of guy you want to face with a bad third-down defense. Since the start of 2013, New Orleans is the league's best third-down offense, converting 43 percent of its opportunities.In those five seasons, the Saints have 58 touchdowns on third down; only the Broncos have more. But it's also a high-risk down for Brees, as New Orleans has 27 third-down interceptions, also second most in the NFL over the past five seasons.That means winning on third down is all the more important for the Bucs defense, and at the center of any substantial turnaround. Two years ago, Brees converted 12 third downs in beating the Bucs 24-17, including a third and 21, third and 13 and third and 11. Last year, in beating New Orleans, the Bucs held the Saints to 4-for-13 on third down, with a late interception."The things that we've got to concern (ourselves with) is keeping them out of the end zone and getting off the field on third down," defensive coordinator Mike Smith. "The numbers show it. We are not very good at either one of those things right now. We've been very inconsistent."Contact Greg Auman at email@example.com and (813) 310-2690. Follow @gregauman.