Defences in modern basketball frequently exchange assignments rather than fighting to maintain them. The change followed directly from an offence built around screens and perimeter shooting.
Screens create a moment of advantage
A screen obstructs a defender so that the ball handler gains a step, and that step is usually enough to create an open shot or a driving lane.
Traditional coverages required the defender to fight over or under the screen while a teammate delayed the ball handler until the assignment could be restored.
Each of those responses takes time, and against accurate perimeter shooting the small delay is sufficient for a clean attempt.
Switching removes the delay entirely
If the two defenders simply exchange assignments as the screen arrives, neither has to travel around it and there is no interval of advantage.
The ball handler faces a defender immediately, and the screener is picked up by the other, so the action produces nothing on its own.
Offences responded by screening repeatedly to force a specific mismatch rather than to create an immediate opening.
The cost is the mismatch
A switch can leave a much taller player defending a quick guard on the perimeter, or a small guard defending a much larger player near the basket.
Offences hunt these situations deliberately, isolating the mismatched defender and clearing space so no help is available.
The defence's answer is either to accept the mismatch for a possession or to send help, which reopens the passing lanes switching was meant to close.
Roster construction changed to support it
Teams began valuing players of similar height and mobility across several positions, since interchangeable defenders make switching viable without penalty.
A player who can guard both a guard and a forward removes the mismatch the offence is looking for, which is why such players command a premium.
Specialists who defend only one position have become harder to field, because the offence will simply screen until they are exposed.
Positions became descriptions rather than roles
With defenders expected to cover multiple assignments and shooters distributed around the arc, the traditional five positions describe height more than function.
Team sheets still list them, but the responsibilities attached to each have converged considerably over the past decade.
What remains distinct is the ability to defend near the basket, which is the one task that still requires a specific physical profile.
