Sheriff’s group’s attitude about James’s end (5)
I believe the answer is:
posse
'sheriff's group's' is the definition.
(historical term for a group assisting a sheriff)
'attitude about james's end' is the wordplay.
'attitude' becomes 'pose' (I've seen this before).
'about' indicates putting letters inside.
'end' indicates one should take the final letters.
The final letter of 'jamess' is 's'.
'pose' going around 's' is 'POSSE'.
(Other definitions for posse that I've seen before include "Group aiding lawman" , "Group of friends together" , "power" , "Troop at the service of a local sheriff" , "Group formed by sheriff" .)