The loser trains for and completes a real half marathon wearing an 'I suck at fantasy football' shirt. Thirteen miles of strangers reading your chest. The training months are the hidden bulk of the sentence.
Heavy sentence
Severity 4 punishments are the ones people talk about for years, which is exactly why they need full league buy-in before week one. Put it in the constitution, set the deadline, and agree on proof requirements up front.
The long haul: this is not a one-afternoon sentence. With a time commitment of several months, the punishment keeps paying out (for everyone else) long after the season ends. Long sentences need a written end date and a league-appointed enforcer who checks compliance.