Foot faults are called by line judges who watch the server’s feet while they are in motion. This can be a pretty controversial fault to call, as demonstrated by the infamous foot fault call against Serena Williams in her 2009 US Open semifinal against Kim Clijsters.
Williams was facing a crucial point at 15-30 down to keep her hopes alive, but the line judge called a foot fault on her second serve.
For more information on how the scoring system works, see our article on how to keep score in tennis.
Foot faults are penalized in the same way as missing a serve would be, so Williams lost the point, and the score moved to 15-40 – break and match point to Clijsters.
Regrettably, Williams was incensed by the call and began berating the match officials; she later apologized. This meant that she was docked another point, therefore handing the match to Clijsters.
Casual observers of the game of tennis might be confused as to why Williams lost her cool over a simple officiating call. However, the fact of the matter is that foot faults are called very inconsistently, meaning that players regularly overstep the line on serve, but are not penalized for it.
Beginners and intermediate players often touch the baseline during serve, even though they may be unaware of it. Of course, it is challenging for the opponent in a typical friendly park game to bring up the subject of a foot fault, being on the other side of the court.
Considering that foot faults are called so sporadically, it’s easier to understand Williams’ frustration at being penalized during such a crucial point in the match.
At the time, a former line judge named Jeff Ponder explained that the line judge would have been correct in her call. He also went on to say that foot faults cannot be challenged or reviewed, and this is still the case in 2019.
Former serve-and-volleyer Justin Gimelstob gave his opinion: “95% of foot faults are not called”. That is why they tend to incite plenty of anger when they are flagged up.