Picture this you're a Olinemen and you pinch to block a outside blitz you're first assignment would be the inside gaps. You try to be aggressive and miss the block, why? because normally on a pass play the Olinemen wait for the guy to come at them if you're aggressive it's more of a chance to miss the block.
Keeping a RB in to block 99% of the time a LB will love to have a RB block them because they are usually a lot smaller and you just bullrush the guy or jump over him when he goes for a cutblock.
The Key to blocking a OLB blitz is to have a TE to that side, first you see the blitz then shift a TE over to that side TE are better at blocking than a RB. Also another easy way to win vs this blitz is to have a WR block most the time if the guy is blitzing the OLB the flats are open if not then he is in a cover 2 and the middle is open.