Maybe one on train's covering away game (5)
I believe the answer is:
rugby
'game' is the definition.
(rugby is a sport or game)
'maybe one on train's covering away' is the wordplay.
I cannot quite understand how this works, but
'covering' could be 'rug' (rug is a kind of covering) and 'rug' is found in the answer.
'away' could be 'by' (synonyms) and 'by' is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for rugby that I've seen before include "English city; game" , "Try game?" , "Game; town" , "Midlands town" , "Team game" .)