I'm trying to think through the physics of the longer-arms bit, and it's tricky. We have two non-rigid bodies colliding. The guy with the longer arms gets some control over the angles at which the two of them apply force, but his discretion is limited by the need to preserve his own balance.
If it matters so much who hits first, why don't see ball carriers making greater use of stiff arms? Stiff arms really seem to work only when they screw up the defenders angle or balance.
NFL Videos: NFL Films Presents: The Stiff Arm is an NFL highlights video of stiff arms. It seems to me that pretty much all of them either:
- Are against guys who lacked momentum and/or balance for the tackle, e.g. because the would-be tackler had just turned 90 degrees to close on the play.
- Served to increase separation between two players (runner and would-be tacklers) moving in pretty much the same direction.
- Really amounted to batting the would-be tackler's arms away.
None of these undermines the theory that when two guys are facing each other straight-up, arriving first with the hands isn't a big deal.