I maintain that he can’t, his teeth would snap out of his gums or get worn down before he got a chunk of the ball out; he says with enough lateral grinding he could saw into the thick rubber and free a piece. What says YOU, dopers?
Why speculate when you can just let him try it? 
A lacrosse ball is very dense rubber but not indestructible. I’ll bet you could chew off a very small piece by the method described. You couldn’t take a big bite like eating an apple.
I doubt it.
I gave my pit bull a lacrosse ball. he worked it for a month before he could break pieces off of it, and I think the only reason he was able to break pieces off it was because it was left outside to be wet by the sprinkler and frozen at night for a couple weeks.
A dog’s teeth are designed for tearing meat. Sticking pointy teeth into the ball might not do more than poke holes in it. I’ll bet a motivated human stands a better chance at “sawing” off a piece when that is the sole objective.
Actually, I would say that a dog’s teeth (or those a lion, hyena, etc.) are very good at slicing/shearing meat and gristle. I imagine that the consensus would be solidly on a dog’s teeth having a better chance at a lacrosse ball - our teeth, jaws, and jaw muscles really are puny compared to your average-sized dog, and it’s no contest vs. a canine with serious chompers like a pit bull.
If a pit bull can’t do it (or does it with difficulty) then I can’t imagine a person having an easy time with it.
As a side note - I wonder how a pit bull compares to a hyena in terms of bite strength?
That’s my point. The dog has huge jaw muscles and a much longer jaw than a human, giving him more leverage to increase the strength of those huge muscles.
I think the hyena would take the contest here, simply being much larger and accustomed to using his teeth to tear prey apart, while my dog has been both bred and conditioned to pull back from using his full capabilities.