He should said "Guys that drink stiff drinks before fights win fights" However, much props to Teddy Atlas. He has a knack for calling out the Glass Jaws, as does Vodka Breath Merchant.
I was thinking along the same line. You normally don't notice a fighters legs being stiff until he glass jaw gets hit.
You see 'stiff legs' on fighters well past their prime age-wise, or fighters who have been KO'd multiple times. They almost look like they're on stilts, something's not quite right in the way they move. They don't bend their knees a lot, they don't do a lot hip movement or rocking below punches and coming back up, their knees look like they're trembling all the time. It's kind of hard to describe, but if you're looking for it you'll know it when you see it. There's a difference in the way an old man walks and a teenager. They both get around just fine, but they do it differently. Think late Terry Norris or Prince Charles Williams. You'll start seeing it on RJJ too, no way he can take this much neurological damage and not start showing it. I can't remember who it was, but there was a high profile fight recently where as soon as the guy came out someone on the announcing crew said 'He's shot, he's got stiff legs' right out the gate and sure enough the guy got whacked out pretty quick. Maybe it was JLC v. Hatton.