he probably just saw a spot where he thought you were weak and made a play. the $12 into ~$20 does let him see you as weak there. if you want to lead turn, make it $20ish. a solid TAG isn't gonna call you PF w/ 4junk from the SB. He might have 77, but I think he makes a smaller CR (if any at all, smooth call is also likely) with a turned boat in that case. i think you're ahead here. if you don't want to play a big pot w/ AK OOP then checking turn behind is fine.