I play Skaven, and I use 3 GRs on defense. I want to develop them:
2 with dodge, block, sidestep and shadowing (or diving tackle if you prefer).
1 with dodge, block, dauntless and strip ball.
The advantage of blodge, sidestep and shadowing: Just stand next to the ball carrier or the ball, and watch your opponent's frustration when he realizes that he can't get away from you with the ball. And on offense, blodge sidestep means that you can run along the sideline without risking getting pushed-out of the pitch. And again, watch your opponent's frustration when his blitz that resulted in a push-back puts you in an even better position to score. And if you position yourself right and your opponent learns the effect of sidestep, in some cases he may chose not to blitz you at all.
blodge, dauntless and strip ball on a MV8 player means that you can play this guy deep in your own zone on defense and be able to blitz any catcher that has the ball in your backfield if he is unprotected. Against a ST3 guy, you only need to roll a 4 with two dice for the dauntless to succeed, so when you are throwing a block, you are almost guaranteed to be ST3. Not a useful skill combination on offense though.
Use your linemen to create TZs so that your opponent can't swamp your catchers. Do the same with blitzers, but try to keep them closer to where the ball is. Then let your turnover machines (i.e. catchers) do their thing.
This strategy is working wonders for me right now.