Since we all seem to have finished bar actually understanding the pairs, I hope you will all forgive my reverting to use of the actual entries now:
It occurs to me that, in pairing the four more thematically conventional "SCARES", one might consider that LE MANS
is, I suppose, technically a RELAY - they do change drivers. This would leave ST LEGER and MARATHON to pair as those "on foot" - albeit not quite in the same sense.
I don't suppose it helps much, since the real mystery is how GROOVE and GINGER pair; oh well, just thinking aloud.