Crossword Genius

Starting the half playing at impossible speed (6-4-5)

Ross

I believe the answer is:

faster-than-light

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

'starting the half playing at impossible' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'speed' is the wordplay.
I cannot quite see how this works, but
'speed' could be 'fast' (I've seen this before) and 'fast' is located in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Irish Times.
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