Since their February 3 loss at Youngstown State, Butler has won 12 straight games and found themselves one more win from consecutive Final Four trips. As this chart shows, the Bulldogs have done it by playing, well, bulldog defense.
Net Efficiency Margin offense (blue)/defense (red) splits (all charts here are 5-game running average NEM)
The offense has stayed about the same, but the defense has improved significantly since that game. They actually played good D at the beginning of the season, but several bad games in January caused the poor spike in the middle. The last nine games in particular have been solid; their average -13.7 defensive NEM over that stretch is roughly top ten quality.
During the tournament, Butler has relied on their defense to carry them this far. Their 11.8 offensive NEM average during the tournament is the lowest of the eight teams remaining. Of course, defense was also how the Butler did it last season, and that worked out pretty well. They may need the offense to pick it up to beat a more well-balanced Florida team.