But, covering the grenade will almost certainly spare others in the unit, whereas attempting to throw it back lacks certainty and an air burst may actually inflict more injuries to the unit. In addition there is the issue of the decision maker possibly being able to estimate the total elapsed time that the grenade has been in view. No easy solutions.
In World War II a baseball player was serving with the Marine Corps. I think it was at the Battle of Tarawa. The Japanese had been lobbing grenades onto the Marine's position, this Marine was lobbing them back.
After three times, the Japanese changed their tactics. They waited a bit before lobbing the grenade. The Marine picked up the grenade, started to throw it back when it went off.
Needless to say, he no longer had a baseball career.