Run "Fits"

For me, run fits are where defensive players "fit" against blockers. Simply, it can be what gap each defender is responsible for covering. However,more thoroughly, I think run fits need to force ball carriers into tacklers. For example, on a typical Pro I power play, the TE and OT, against a 50, will double the DT to the PSLB'er, and the FB will kick out the DE. Technically, I suppose you could say that the DE collisions the FB and "covers" C gap. However, this is where "run fits" come in. If he collisions the FB with his inside shoulder, he leaves one extra gap inside that the ball carrier can squeeze through if the Strong Safety stays to the outside. So, if the DE "fits" the FB with his outside shoulder instead, he closes that gap and forces the Ball carrier to the outside where the SS is unaccounted for in the blocking scheme.

In another example, on toss if the contain player takes on a pulling guard with his inside shoulder to "contain," an alley opens up between him and the next inside player. Here, a FS can be used to "fit" into the alley. Thus, the contain player leverages the Ball Carrier inside where he can be tackled by the FS filling the alley.