What are the stack sizes? I would consider raising the flop depending on stacks. 4-handed, he could be leading weaker 9s, gutshots, or 34s. If he's got something like K5s, he's like 9-1 to hit the turn with some implied odds. I'm assuming an aggro player is going to have some bluffs in his range and we might want to call him down a little lighter on future streets. A9 TPTK is a monster 4-handed.
Looks like a fairly obvious call to me. The hands that beat you are too unlikely. If he shows up with a straight he is calling to loose preflop, if he has a set he shouldn't be donking the flop. If the river was a diamond and he has something like Td9d and backed into a flush it's just a cold deck. There are hands he could be raising for value that you beat, Q9s and A5 are both possible.
