I reads like you want the users to select 1 event from the list. So, why don’t you use 1 Single Choice question? The information “I won’t take part in the other 4 events” is not really relevant, is it?
Add actions to the radio buttons:
Action: Modify variable
Value: 1 (for the first), 2 (for the second)
The LMS will save the score and you’ll know that a user who scored “1” has selected “Event 1”.