Just one question why call grenade in the 1st place, we only allow actual tornado grenades to be used as grenades. We had considered Bright Red Tennis balls as an alternate but figured tornadoes made more sense.
If you are using an item like a tennis ball then, I am on the side of the make sure it is a grenade before you call your self out. We have had people toss expended grenades in a building to flush people out, as well as chunks of wood.
You have to be aware of what is happening around you.