Nevertheless, chum climbs into a four-in-hand (5-2)
I believe the answer is:
tally-ho
'a four-in-hand' is the definition.
(I've seen this before)
'nevertheless chum climbs into' is the wordplay.
'nevertheless' becomes 'tho' (informal spelling of 'though').
'chum climbs' becomes 'ally' (I can't explain this - if you can you should give a lot more credence to this answer).
'into' means one lot of letters goes inside another.
'tho' enclosing 'ally' is 'TALLY-HO'.
Can you help me to learn more?
(Other definitions for tally-ho that I've seen before include "Hunt cry" , ""I've seen the fox!"" , "Come on, hounds!" , "Huntsperson's cry" , "Hunter's cry" .)