Neyartha seems to have had a good round of Golf before setting this one.
ACROSS
1 Young French men in front of the Austrian university are steeped in fury (8) IMMATURE {I{MM}{AT}{U}RE}
5 Adapt to religious books holding control after internal turmoil (6) ORIENT {R(E<=>I)N} in {OT}
9 Suspicion that Lee's FBI ID has been compromised (9) DISBELIEF*
11 Evil spirit's golf score (5) BOGEY [DD]
12 Husband following revolutionary Greek character's account boards a ship to get some shrubs (7) SUMACHS {S{MU<=}{AC}{H}S}
14 Go on a binge and cause an undesirable temperature rise by removing a gas (7) OVEREAT OVER
15 Herb causing problems for the fast cat? (8,4) LEOPARDS BANE {LEOPARDS BANE}
17 Stem missing? Niece's experiment design reveals a lack of familiarity (12) INEXPERIENCE {NIECE
20 Enrage and blow up the Frenchman's replacement for the model (7) INFLAME INFLA(-t+m)ME
22 Belligerent letters from a ghost? I let those slide (7) HOSTILE [T]
23 Piece of dug-out turf found by Tesla and a Roman poet in retreat (5) DIVOT {T}{OVID}<=
24 Purposeless manipulators? (9) TWIDDLERS [DD]
26 Attempts to start off with clues about an animal from the east (6) ESSAYS {
27 After the loss of the opener, retreats to the exits (8) EGRESSES
DOWN
1 Process the salt with the heads of the Indian Oil divisions in sunny Erode (6) IODISE Acrostic
2 Monk's mule made dizzy by a large juicy fruit (9) MUSKMELON*
3 Drink, reportedly, to get support for a golf ball (3) TEE (~tea)
4 Recall upset band surrounding the new council workers (13) REINSTATEMENT {N}{STATE}{MEN} in {TIER<=}
6 Pieces of elastic are Barb's burden at sea (6,5) RUBBER BANDS*
7 Head out with a hound dog to get a bird (5) EAGLE
8 Regularly ignored places under evaluation for romantic meetings (6) TRYSTS {TRY}{S
10 Is it needed to see the deluge? (13) FLOODLIGHTING [CD]
13 Mysterious hot cup's X-ray reveals dough for an eclair (5,6) CHOUX PASTRY*
16 Want decay with nitrogen instead of sulphur initially (9) NEEDINESS (-s+n)NEEDINESS
18 Score in golf with some badminton equipment? (6) BIRDIE [DD]
19 Toxic condition of an Oriental with second thoughts on one employed by the Secret Service (6) SEPSIS {S{E}{PS}{1}S}
21 Ball game featured in a face-off? I've seen that (5) FIVES [T]
25 Colouring agent found in the auditor's metal-shaping device (3) DYE (~die)
GRID