This movie is about a married man killing a beautiful woman, because she is pregnant with his child. Why is it called Match Point?
The character wants to disguise his murder as a robbery. He gets rid of the loot (jewellery) by launching it in the river. However an item just touches a barrier, and it can fall on one side or the other.
This will decide the fate of the man, and it is the same situation as when a tennis ball, during match point, touches the net and pure luck will decide outcome of the game.
The title of the film is simply a play on words.
The main character, Chris Wilton is a retired Tennis Professional. The fact that he murders his mistress and gets away with the crime is considered Match Point.
Simple Definition of match point in tennis terms defined by Merriam-Webster Dictionary:
: a situation in tennis in which one player or team can win the match by winning the next point
: the final point that must be won to win a match in tennis