My definition for cheap shots is the same it's always been. Anything after the whistle is cheap. Anything intentional out-of-bounds is cheap. Crack blocks, taking out the knees, intentional helmet to helmet, facemasks.
Basically it's anything that shows "intent to injure".
Steeler fans like tough, physical ball. We like it when players lay the wood, get blow'd up, and trucked. We even congratulate other teams when they lay a particularly good hit on one of our guys.
But we don't like seeing people leave the field on stretchers. No grudge when it happens accidentally, but we hate dirty play.