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

Calling a late jam

Pre-flop
Blinds 400 / 800 (100 ante)Pot 12,100 (15.1 BB)Your M = 6 • Orange zoneBBA♣9♣● 12,600 (15.8 BB)YOUto actBTN● 10,000 (12.5 BB)Short buttonall-in 10,000 (12.5 BB)SBfoldsD

A button short stack open-jams about 12 BB, the small blind folds, and you cover, holding A♣9♣ in the big blind.

A button open-jams ~12 BB; you hold A♣9♣ in the BB and cover. Best?

WhyA button open-jamming twelve big blinds is doing it with plenty of trash, not just premiums, and against that range A-9 suited is comfortably ahead while you close the action at a fair price. Fold this and you let a wide stealer run you over - the same hand you'd release to an under-the-gun shove is an easy call here.
What happensYou call and get it in ahead of his range. Against a late-position jam, folding hands this strong just hands the button free chips.
The looser someone shoves, the looser you call - and nobody shoves looser than a late-position steal. Calibrate your call-off to the jammer's position, not to some fixed 'good enough' hand.

Position widens both sides of the equation - a jam from late position comes from a wide range, so the range that profitably calls it widens to match.