This was my first thought as well. Let's see, how can you fix that? So, they make an accessory that is roundish. Maybe it even has slots for weight inserts, so you can adjust how heavy it is. It has multiple easy ways to clip it to your person. You need to be able to pull it off your body, and throw it, but it doesn't go break a fucking window. So...maybe there's a cord attached to it, and that goes to a small winch with an electric motor, and as soon as you release, it wheels it back in, while also recording the velocity the in-game grenade should have?

Problems I see with this are:

• You don't want to feel the cord as you pull it free and lob it. So it can't have a taut cable attached to it all the time, there needs to be some slack. But maybe the slack is just long enough that once it leaves your arms reach, it is pulled tight and activates the return motor?
• What is the return motor attached to? Is there a tripod with a 8 foot pole attached to it, and the grenade is pulled to that? What if it was attached to your body, so it would always not get too far from you, and wouldn't require excessive set up? But then, once you throw it, you would feel the weight of the grenade being pulled back towards you, which would break immersion. How do we A) keep it from flying off and breaking shit, B) not negatively impact the immersion, and C) not require excessive setup before playing. And also I guess D) make it work in a small area so you don't have to go find a big space to play?
• What if you have more than 1 grenade in the game? How does the projectile magically get reattached to your belt after you throw that first grenade, so you can throw your other 3 in succession?

I have the questions, but I sure don't have the answers. But I'm equally sure I'm not the first person to try to work through them. I wouldn't be surprised if other people have already come up with these questions, and they were paid to think of them, unlike me.