1-2 NL. 8 dealt, 1 call, 4 fold, dealer raises to $10. Small blind goes all in for $12.50. Big blind folds, guy who called decides he's going to shove $32 all in. Is this legal? Can you reraise when someone goes all in for less than double the original bet + blinds? Is it legal for the small blind to go all in if his all in isn't at least $8 more than the original bet, $18? This confused me because if someone bets $8 more than the blinds, doesn't the next raise have to be at least $8 on top? I understand a short stack can call if his stack is less than the bet, but can he go all in for a little more than the original bet, and if he can, can someone behind reraise?
Possible duplicate, but in short, yes, because the raise from the button is what re-opens his option to re-raise.
If you were to switch it around, where the mid position raised, button called and SB went all-in for less than half the raise, the button would not be able to raise if the mid position just called.