All-court players have aspects of every tennis style, whether that be offensive baseliner, defensive counter-puncher or serve-and-volleyer. All-court players use the best bits from each style and mix it together to create a truly formidable tennis style to play against. In game situations, they have the ability to select an action usually executed by one tennis style. They usually have an attacking game, mixing some groundstrokes and volleys to keep the opponent guessing. Most all-court players won't rush the net immediately after a serve like a typical serve and volley player would. However, their game often revolves around "constructing" a point to where they will be able to approach the net and put away an easy volley or pulling their opponent into the net and hitting a passing shot. They are very versatile; when an all-court player's baseline game is not working, he may switch to a net game, and vice versa. All-court players have the ability to adjust to different opponents that play different styles easier than pure baseliners or serve and volleyers. All-court players stereotypically have the speed, determination and fitness of a defensive counter-puncher, the confidence, skill and flair of offensive baseliners and have the touch, the agility around the net and tactical thinking of the serve-and-volleyer. But just because the all-court player has a combination of skills used by all tennis styles doesn't necessarily mean that they could beat an offensive baseliner or a defensive counter-puncher or even a serve-and-volleyer. It just means it would be more difficult to read the game of an all-court player.
