used when a
sports person at an elite level is intimidated by the situation (finals, quarterfinals, semifinals, etc.) and hence puts in a bad performance, a disasterclass.
this sportsperson usually looks like the real
deal at stages of the competition when the expectation to perform isn’t as strong, like the first few weeks of the league season
can also be used to describe the most elite levels in
sports (Champions League knockout stages, World Cup, Qualifying for any Grand Prix, etc)