Crossword Genius

In fact, join a new league? (6)

Ross

I believe the answer is:

really

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

'in fact' is the definition.
(synonyms)

'join a new league?' is the wordplay.
I cannot quite see how this works, but
'join' could be 'ally' (I've seen this before) and 'ally' is located in the answer.
The remaining letters 're' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for really that I've seen before include "Actually, no kidding" , "Undoubtedly" , "Actually, honest to God" , "without a doubt" , "Dead" .)

I've seen this clue in The Guardian.
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