Crossword Genius

It is over where boxers appear to be running out of energy (6)

Ross

I believe the answer is:

tiring

I'm a little stuck... Click here to teach me more about this clue!

'boxers appear to be running out of energy' is the definition.
I can't judge whether this defines the answer.

'it is over where' is the wordplay.
'is over' says the letters should be written backwards.
'where' becomes 'ring' (I can't explain this - if you can you should believe this answer much more).
'it' in reverse letter order is 'ti'.
'ti'+'ring'='TIRING'

Can you help me to learn more?

(Other definitions for tiring that I've seen before include "Causing weariness" , "Becoming sleepy" , "Boring" , "Wearisome" , "Laborious" .)

I've seen this clue in The Times.
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