At the Refuel Event, a few dozen 14-50 receptacles were provided for charging. I never needed to leave the track to Supercharge.
I was at Corsa4, which had the 14-50 available. 14-50 only get you 10~12% charge per hour, depends on the generation of MCU you have. I suppose if you do fewer laps or more leisurely pace you could milk the 14-50 all day and be happy. For most people, a track session consumes significant more charge than the 14-50 can replenish between sessions.