The key to stopping the run and maintaing gap control and using your Defensive Line stunts. By shifting the line towards the play can stuff runs between the tackles. One play that I use for my Zone Blitzes/Run Fits is the Crash 3 play from the Stack.
Say that the opponent comes out in your Basic 21 Personnel (2 RB 1 TE 2 WR). Shift the Line to the 3 Man surface (IE:Tight End side). Its probably best to user the Blitzing MLB just sto stuff anything coming through the line. If they try to take it off tackle, You'll have the SS out on the edge crashing in. And Usering the MLB will allow you to kill and fill any cutback lanes.

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