How can I protect myself during a soccer game when my stitches were recently removed?

You can't. It depends on location of wound. If incision is on the legs and were recently removed its better to wait until the incision is sealed and water tight. Even though the stitches were removed the strength of the underlying tissue woud not withstand significant shear force.
Tape. Steri strips applied with adhesive can help protect a recently repaired laceration from further trauma.