Force's colonel hosting first of military exercises (6)
I believe the answer is:
compel
'force's' is the definition.
(I've seen this before)
'colonel hosting first of military exercises' is the wordplay.
'colonel' becomes 'col'.
'hosting' means one lot of letters goes inside another (inserted letters are welcomed in or hosted).
'first of military' becomes 'm' (1st letter of 'military').
'exercises' becomes 'pe' (Physical Education).
'm'+'pe'='mpe'
'col' placed around 'mpe' is 'COMPEL'.
(Other definitions for compel that I've seen before include "Bring about by force" , "Use force, oblige" , "Use force or influence to make something happen" , "Urge on, force" , "Coerce, force to obey" .)