They have faith in Gunners – with group of footballers blocking big shot and Isak’s header (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

RA(abbrev. for the Royal Artillery, the branch of the British Army providing firepower/nicknamed “The Gunners”) plus ( with ) [ FA(abbrev. for the Football Association, a group of footballers) contained in ( blocking ) STAR(a big shot/a celebrity) ] plus ( and ) 1st letter of ( …’s header ) “ Isak ”. Defn: …/practitioners of the Abrahamic religion, Rastafari.