There are a few ways to fix a crack in a tennis court. One option is to fill the crack with a sealant or adhesive. Another option is to patch the crack using a concrete patching compound. A third option is to resurface the entire tennis court.

Fill the crack with a polymer based caulk. The caulking will fill in the space and prevent water from seeping into the crack and causing more damage. It's a good idea to use a polymer-based caulk because it will flex with the surface of the court, which will help to prevent future cracks from forming.