The return position is a bet about which serve is coming

What depth actually buys

A returner standing well behind the baseline gives the ball more time to travel, which converts a marginal reaction into a manageable one. The extra distance also lets the ball drop from its peak, so a delivery that would have been struck above shoulder height can be met comfortably. The cost is that the ball has spread wider by the time it arrives, so a serve angled into the corner pulls the returner far outside the court.

From that position the return must travel a long way to land in play, which gives the server time to move forward and take control. Depth therefore solves the problem of contacting the ball at the expense of the problem of what happens next.

What stepping in costs and gains

A returner who moves inside the baseline takes the ball earlier, before the angle has fully developed and before the bounce has reached its height. That compresses the server's effective margin, since a serve that would have pushed the returner wide now arrives while he is still near the middle. It also shortens the server's recovery time, because the return travels back over a shorter distance and arrives sooner than expected.

The price is that the returner must commit to a direction before he has full information, and a good server will punish an early commitment. Stepping in is therefore an aggressive bet rather than a general improvement, and it is only correct against specific serves.

The second serve changes the calculation

A second serve arrives slower and with more spin, which gives the returner enough time to move forward without guessing. That is why returners who stand deep on first serves will often be found several steps inside the court on the second. The movement is visible to the server, who then faces the choice of accepting a defensive position or attempting a riskier delivery.

Servers who respond by increasing pace on the second serve are trading double faults for the return position they surrender otherwise. The negotiation over that single ball accounts for a large share of the pressure in any close service game.

Reading patterns rather than the toss

Returners rarely predict the serve from the ball toss, which is deliberately consistent in any player who has been coached properly. What they read instead is pattern: which serve a particular opponent prefers at particular scores and from which side of the court. Those tendencies are stable enough within a match to be worth betting on, even when the player is aware of them and tries to vary.

Committing to a pattern means being wrong occasionally and comprehensively, which is why the tactic looks foolish in the moments it fails. Over a long match, however, guessing correctly on the important points is worth far more than being marginally late on all of them.

Why the position is itself a message

Where a returner stands is visible to the server long before the ball is struck, and servers adjust their intentions accordingly. A returner who moves deep invites the server to take pace off and add placement, since raw speed is being neutralised by distance. A returner who crowds the baseline invites the body serve, which is the delivery that punishes a player who has removed his own space.

Because both parties are reading each other, the position becomes a bluff as much as a calculation, and it can be changed between points to mislead. The most effective returners vary it deliberately, ensuring the server never settles into a rhythm built on a stable expectation.