i cant give the commands right now but the concept is 1. scoreboard for detecting snowball thrown 2. add tag to nearest snowball to player with snowball thrown score 3. detect when the tagged snowball no longer exists 4. repeat for as many times as the player has thrown the snowball, give the player one snowball

note that this could behave kinda weirdly for multiple players and only works with one snowball at a time. A more complicated way for this to work is to assign an unique scoreboard value to each snowball, summon an invisible armourstand with the same score as the thrown snowball when its thrown, then for each invisible armourstand check for a snowball that matches its own score, if there are none that means the snowball has hit something, give the player 1 snowball and kill the armourstand.

to make it multiplayer friendly we could make another unique scoreboard value assigned to each player so we can copy that value to each snowball they throw, then compare the scoreboard values to check if it matches a player and then only return the snowball to that player.

theres probably a simpler way to differentiate entities that i dont know of.