Merciless leader restricts team socialising (6)
I believe the answer is:
mixing
'merciless leader restricts team socialising' is the definition.
I can't judge whether this defines the answer.
'merciless leader restricts team' is the wordplay.
'merciless leader' becomes 'ming' (I can't explain this - if you can you should believe this answer much more).
'restricts' is an insertion indicator.
'team' becomes 'XI' (a football team, from Roman numerals for mm).
'ming' going around 'xi' is 'MIXING'.
Can you help me to learn more?
(Other definitions for mixing that I've seen before include "it's done by a whisker?" , "Mingling" , "Combining to form one substance" , "Blending" .)