[DougOzzzz]

Using data from NFL games from 93 to 04, I get 94.837% of the games that a team managed to cover the spread +21 points. I'm not sure how ties effect this bet, but I will ignore them for now.

Anyway, the probability of winning this is simply .94837^10 or about 58.85%. That's not enough to make it profitable (needs ~63%) but it's not impossible that if your friend picks the correct 10 sides that it could be +EV.

Frankly I'm a little surprised because when I read this I thought it would be a much bigger "suckers" bet.

Edit: What are the rules on ties? This could have a pretty significant effect, and if "ties lose" is the case, the win pct drops to 55.3%.