I'm glad no one's said "fold."
Yup, it's a clear raise. The SB who capped preflop is not a maniac, but this is AK some portion of the time, and for those times I desperately want the CO out of "my" pot. So I raise, give him two bets to consider, and hopefully he'll fold.
There were no decisions left to make in this hand that didn't make themselves after that raise, but for those of you who want to know how it played out:
Limit Holdem Ring game
Pre-flop: (6 players) Hero is BB with 9♦ 9♠
2 folds, CO calls, Button folds, SB raises, Hero 3-bets, CO calls, SB caps, Hero calls, CO calls.
Flop: 8♠ J♣ 7♦ (10.5SB, 3 players)
SB bets, Hero raises, CO folds, SB 3-bets, Hero calls.
Turn: 6♠ (8.25BB, 2 players)
SB bets, Hero calls.
River: 5♦ (10.25BB, 2 players)
SB bets, Hero raises, SB calls.
Final pot: 14.25BB