Detecting whether a snowball in minecraft is broken after its been thrown
Solution 1:
A simple answer is by Dragnoz's contraption he made. This is making deadly snowballs but it still shows you a way of tracking the snowball.
The simple way to track it is as follows:
/scoreboard players add @e[type=Snowball] Ball 1 where Ball is a new dummy object.
And then an easy way you can do it is hook the command block up to a comparator and when it doesn't give a signal, you reverse it with a redstone torch and activate your command. Depending on your knowledge, the other way might be far to complicated for you, no offense.