Betting organisation taking on the established leaders (4)

I believe the answer is:

tote

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

'betting organisation' is the definition.
I can't tell whether this defines the answer.

'taking on the established leaders' is the wordplay.
'leaders' indicates taking the first letters.
The first letters of 'taking on the established' is 'TOTE'.

Can you help me to learn more?

(Other definitions for tote that I've seen before include "Carry; betting device" , "transport" , "holdall" , "Carry (a gun)" , "Capacious bag or basket" .)

I've seen this clue in The Irish Times.

Want a hint initially instead of a full solution? Install my app