The Tampa Bay Buccaneers had a conservative offense in 2015. Or at least, they did in conventional terms. They just loved the running the bal. Thomas Bassinger tabulated some of the key statistics, and concluded that the Bucs ran on 57.1% of all first downs over the season -- that's fourth in the NFL. That sounds like it would be too much, but the Bucs also gained a league-high 6.24 yards per play on first down -- apparently, their first-down strategy was working.
I've seen murmurs that this changed in the final four games of the season, when the Bucs dropped from 6-6 to 6-10, but that isn't quite true. The effectiveness of first-down plays dropped to 5.66 yards per play, but that still ranked 11th in the NFL. And that happened despite the team running the ball less: the Bucs ran the ball just 45.4% of the time on first downs in the final quarter of the season.
That may in part be explained by having to play catchup, but most of the drop in efficiency can be explained because the offense as a whole became less efficient. Dropping back to pass resulted in 7.05 yards per play over the final four weeks, compared to 8.50 yards per play over the first twelve games. But the Bucs ran the ball at 5.1 yards per carry the first thirteen weeks, and just four yards per carry over the final four weeks. Passing is always more efficient than running the ball in terms of yardage, of course, but running the ball can set up the pass as well as providing more consistency than passing.
Regardless, there doesn't appear to have been anything fundamentally wrong with the Bucs' first-down strategy at least in terms of run-pass balance. Instead, the offense as a whole collapsed over the final four weeks of the season, which undoubtedly contributed to Lovie Smith's firing. Perhaps one reason that happened: Vincent Jackson was out for 3.5 of the four games.