If you spam backspace to repeatedly drop multiple tools, at some point one will get stuck in your hand, but you’re not registered as actually having it equipped. When this happens, the tool will appear to be a member of the Workspace, but there is still a RightGrip weld in the character’s Right Arm keeping the tool attached. Even though the glitched tool is not a member of Backpack, it will still appear in the Backpack GUI, and equipping the tool again will bring it back to normal behavior.
With the glitched tool attached to your hand, you can then “pick up” another player’s character by running into them with the tool. The other player will equip the glitched tool since it’s in the Workspace, but since it’s still welded to your arm, you will pick the player up.
The other player can unequip the tool to end this glitchy behavior.
This is easiest to reproduce with many tools available, but I believe it is possible to do with just 2 or 3 tools.
I’ve attached a repro place, easiest way to perform the glitch is by running in a line while dropping lots of tools in front of you, re-picking them up as you go. I’ve colored them all differently, so when you see z-fighting, you’ve got 2 tools in-hand at the same time.