Sliding into a shot in tennis has almost always been commonplace on a clay court, the slippery nature of the surface meant players were almost required to slide in order to recover effectively. Sliding on a hard court however, is something that has only appeared in the last 15-20 years. So why are players sliding, what's the advantage of doing so and how has it changed the game?
First we have to look back to how tennis looked before everyone started sliding around like maniacs. Here we have the traditional, on the run, change of direction courtesy of Pete Sampras. On both sides he makes contact in a closed stance, and afterwards stops, turns around and recovers.
The fundamental disadvantages of this is that he has to take additional steps before and after the shot. Going into a closed stance requires lots of small, adjustment steps, which means more time needed to set up. The steps that he takes after the shot are required for him to stop his momentum before he can change direction. In contrast the modern players can plant their outside leg in one big leap in a semi open/open stance. The slide allows players to simultaneously stop and make contact with the ball. This means a player is ready to push back off that outside leg and move back to middle of the court almost immediately following contact. Not only does this streamline two movements into one but it also has some biomechnal advantages, such as a wider base allowing for more rotation in the upper body whilst on the run.
This evolution of movement has produced baseliners who are much harder to get out of position. This has made attacking much more difficult and is in part why we have seen more counter punchers be effective over the last twenty years. Put simply this evolution has enabled the the more athletic modern players to retrieve balls, that historically would have been un-retrievable. The attacking shots which used to create space don't have quite the same impact as they did in previous generations. It also allows players to hit offensive shots in situations that historically would have been defensive.
Another interesting aspect of this evolution is the emergence of taller players who move exceptionally well. It used to be accepted that taller players would have great serves but be generally clunky around the court, a bit like Isner or Karlovic. This seems to have changed, the average height of the top 10 ATP players has increased over the last ten years and despite the players getting taller you can argue the players are moving better. Zverev, Tsistipas, Hurkacz and Medvedev are all over 6'5 and are some of the best movers in tour. The top ten players are 3 inches taller than the your average, top level tennis is getting taller. This video is of 6'5 Hurkacz moving brilliantly.
The evolution of movement serves as a great example as to how much the game has moved forwards in a relatively short space of time. With Nadal and Djokovic acting as the trailblazers, the next generation of players coming through have done well to adopt these movement techniques in a relatively short space of time. The evolution of sliding on a hard court has shaped the last two decades of tennis much more than many realise.