Lanky schoolfriends as a group play regularly (6)
I believe the answer is:
gangly
'lanky' is the definition.
('gangly' can be a synonym of 'lanky')
'schoolfriends as a group play regularly' is the wordplay.
'schoolfriends as a group' becomes 'gang'.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternate letters of 'play' are 'ly'.
'gang'+'ly'='GANGLY'
(Other definitions for gangly that I've seen before include "Tall, thin, awkward" , "Loosely-built, lanky" , "Tall and awkward in movement" , "Tall and spindly" , "With long, awkward limbs" .)