It depends.
If your employer is aware of and has gone along with this kind of activity in the past, then your injury may be considered in the course of the employment. Similarly, if you were horsing around but stopped so you could get back to work, and the other person kept messing with you leading to your injury, you may meet the standard.
In other words, if you were the innocent victim of another person’s horseplay, or if your employer allows the horseplay to proceed without intervening, the injury may be compensable. Otherwise, a worker injured while participating in horseplay is not entitled to worker’s compensation.