[bxpeter]

Since DERB 3-bet preflop and then went with check-call on the flop and turn (i have no clue what thats all about), he can't give his opponent credit for anything. I think he would have just check-called the river if it didn't put that 4-straight out there. But now, ace-high probably won't value bet and its very unlikely that the oppoenent will bluff raise him. Given Derb's image he probably expects that many players will call with ace high.

So, vs. checking the river, he gains a bet when ace-high calls and loses the same if opponent has a better hand. (I assume derb doesn't fold on the river if he checks)