Defensive Penalties

In the last post, I discussed a new model for season wins based on some revised variables. Two new variables I added to the model were offensive penalties and defensive penalties.

The model shows that holding all other variables equal, the coefficient for defensive penalties is positive. This is unexpected. I redid several models, and anyway you slice it, more defensive penalties correlate with more wins--in terms of both number of penalties and penalty yards. Keep in mind that correlation does not equal causation, but it's hard to imagine why a team that is winning would be likely to commit more penalties when on defense. The effect is not severe, but it is definitely significant.

In contrast, offensive penalities correlate negatively with winning in all models. This makes sense.

What could the explanation be?