Defending the pick and roll: drop, switch and hedge
Defence
The three main coverages against a ball screen, what each one gives up on purpose, and how to recognise them live.
Almost every half court possession includes a ball screen, so almost every defensive scheme is really a decision about how to guard one. There are three common answers, and each concedes something deliberately. Knowing which one a team is using tells you what shot they are willing to allow.
Drop coverage sends the screener's defender backwards toward the basket while the guard's defender fights over the top of the screen. The big man sits in the space between the screen and the rim, protecting the basket and waiting for his teammate to catch up. What it concedes is the pull-up jump shot from around the free throw line. Against a guard who cannot make that shot, drop coverage is close to free.
Switching trades assignments: the big man takes the guard, the guard takes the big man. Nobody is ever beaten by the screen because nobody has to go around it. What it concedes is a mismatch, usually a smaller player defending a bigger one near the basket, and the offence will immediately throw the ball there. Teams that switch everything need five players of roughly similar size, which is the main reason that style of roster became common.
Hedging, sometimes called showing, has the screener's defender jump out hard at the ball handler for a moment, forcing him sideways and backwards, then scramble back to his own man. It buys two seconds of chaos and costs two seconds of exposure: during the recovery, the roller is briefly unguarded, and a weakside defender has to rotate across to cover him. That rotation is where most open corner threes come from.
A fourth option exists and you will see it against non-shooters: going under the screen. The guard's defender cuts behind the screener instead of chasing over the top, arriving in front of the ball handler and daring him to shoot. It is an open insult and a perfectly good tactic.
To identify the coverage live, watch the screener's defender only. Backpedalling means drop. Stepping out and staying means a switch. Lunging out and sprinting back means a hedge. One possession is usually enough to tell.