I cannot say I have ever seen aggression in african clawed frogs.

They do tend to bite first and ask questions later when feeding is concerned. I have seen my frogs accidentally bite one another when being fed but it's never been malicious and never seen an injury from it. They have no teeth, so they can't really damage anything with their bite.

As far as damage to their webbing, that seems common, every frog I've kept so far has managed to damage their webbing somehow. I had one just rip his webbing in a tank with a single ceramic log (no sharp edges) and a small fluval internal filter.. how I do not know but it always seem to happen at least once a year. The webbing does seem to fully heal slowly but it does heal after a month or two.