I'm a huge Tyson fan, and Lesnar is a gigantic tool, but I'm stunned this is even close. It's not easy to hit a grappler with a punch - they're exceptionally good at deflecting punches and not taking hits in order to close the ground and get a hand on their opponents. And once it goes to ground, it's completely over.
This. I'd bet my next 3 months pay on Lesnar.
someone else said it above.
A fight goes to the ground when either one of the people involved want it to. There's no way Tyson is going to sprawl or stuff a Lesnar shot. NO WAY. Lesnar wins this fight 95+ times out of 100. Tyson may be able to connect on a KO shot on a level-lowered, chin-tucked shooting Lesnar, but it would be a miracle.
Also, not claiming either one of these guys are in their prime or world champions, but James Toney has entered the UFC and is fighting Randy Couture at the end of August at 118. Those of you who think boxers will do well outside of the context of a boxing ring, tune in and see. I predict Randy Couture by nutsmothering submission in round 1.