The tight reg who starts playing more hands late in the session is tired, not loose. His decisions are getting worse, not better. His late-session range looks wider but his execution is weaker.

Why they do it

Fatigue affects tight regs at $1/$2 the same way it affects everyone else - they just hide it better at first. After four or five hours they start playing hands they normally wouldn't, calling in spots they'd normally fold, and making decisions on autopilot. Their late-session game is a ghost of their early-session game.

The adjustment

Attack them more in late position. 3-bet them lighter. Their late-session folds come more easily than you'd expect from a reg. Fatigue makes everyone a worse player.

What it's worth

Adjusting your aggression against a fatigued reg in the last two hours of a session adds $60-100 in spots that simply weren't available four hours ago.