Non-repeatable skills are those that can't be executed with any kind of consistency:
In baseball, situational hitting and pitching are what we frame as non-repeatable. You can consistently throw hard, run fast, show range in the IF/OF, hit the ball hard, or throw strikes. You can't consistently hit above your skill level in pressure situations (but you can hit worse), throw harder in pressure situations, have more range in pressure situations or run harder in pressure situations.