If toolWielder becomes the arrow, and arrows a technically a pickup, you should be able to decode the arrow string and read the account ID of the last player that picked up the arrow.

Unfortunately by the time you get this event the arrow will have been destroyed.

There are many situations where I wish the string information was available _on the event itself_ because of this timing issue. For example, the event (I swear this existed at some point) should contain the string of the potion drank, because is not enough information.

honestly, this could be a reason arrow pvp damage is weird. it might not know who to give the in-combat effect or value to, so it doesn't know what to do and doesn't do any damage, also could be why, at least in the past, you could damage players with arrows if you two were already in combat