Flop Analysis
Flop comes 9s 4s 7c, no flush possible, and we’ve got an overpair with JJ. CO has a slight range edge here and this texture is semi-wet with a spade draw, so we don’t want to blast off our stack. Theory likes checking JJ a lot on this board and, when we do bet, using a medium or large size rather than jamming. The 84BB shove is too big and too polarized; we fold out a lot of worse hands and get called by 9x, 7x, sets, and strong spade draws, while giving up our ability to check back and realize equity when we miss turns.
Note: Jamming 84BB on the flop with JJ is too big and too polarized; checking or using a medium/large bet is higher EV.