Part: Part Nine - Inflection Points: M, Q & the Zones

The re-shove

Pre-flop
Blinds 400 / 800 (100 ante)Pot 3,900 (4.9 BB)Your M = 5 • Red zoneBTNA♠10♠● 10,500 (13.1 BB)YOUto actCO● 18,000 (22.5 BB)Openerraises 1,800 (2.2 BB)SB● 18,000 (22.5 BB)posts 400 (0.5 BB)BB● 18,000 (22.5 BB)posts 800 (1 BB)D

Red zone (M ~5). A player opens to 1,800 from the cutoff and it folds to you on the button with A♠T♠.

Short (M ~5), a cutoff opens, you hold A♠T♠ on the button. Best?

WhyThree-bet jam. Short-stacked you can't flat and play a flop - re-shove over the opener for fold equity plus a strong hand when called. A-T suited is well within a re-jamming range at this depth, and the open created dead money worth attacking.
What happensYou re-jam; the opener folds.  The re-shove collects the pot and dead money.
When you're short and someone opens, the re-shove (three-bet all-in) is your play - you can't profitably flat, so you jam over the open for fold equity and equity.

Short-stacked facing an open, re-shove (three-bet jam) rather than flat - you get fold equity plus equity, and can't play a flop anyway.