Across:
1 Lead actor’s (lead ‘Actors’ = A-) prop (prop) shot (= anagram indicator) (prop = -PPRO-) mystery man (-X) (APPROX) in local ball park? (local ‘ballpark’ = APPROX),
4 Share a tent (camp) starting off (c) (‘camp’ without ‘c’ = AMP-) near Knock (hit) briefly (t) (‘hit’ without ‘t’ = -HI-) overlooking (= reverse indicator) bank (AIB = -BIA) (AMPHIBIA) with class of swimmers (AMPHIBIA),
9 A quarrel (a rift = A-RIFT) over tip for Derby (tip for ‘Derby’ = -D-) (ADRIFT) off course (ADRIFT),
10 Dracula (COUNT-) is (is = -I-S) found around bottom of Kildare (bottom of ‘kildarE’ = -E-) (COUNTIES), Kilkenny and Waterford, for instance (COUNTIES),
12 Is the butt of a joke (APRIL FOOL) after march (APRIL) taking local dope (local ‘dope’ = FOOL) (APRIL FOOL),
13 Put up (ERECT) with nice father (Nice/French ‘father’ = pere) losing the head (p) (‘pere’ without ‘p’ = ERE-) on court (-CT) (ERECT),
14 American (A-) guy (-CABLE-), Pole (North = -N-) and Oriental (East = -E-) found in address (Miss = -MI-SS) (AMICABLENESS) that’s the epitome of friendliness (AMICABLENESS),
18 The New Yorker (AMERICAN) cover (FILM) (AMERICAN FILM) of The Zapruder Tape (AMERICAN FILM),
21 Miracle man loses relic (‘miracle man’ loses ‘relic’ = maman = AMMAN) from middle-eastern capital (capital of Jordan AMMAN),
22 A (A-) verbal onslaught (-RANT-) in revolutionary (= reverse indicator) fiction (sham = MA-HS) (AMARANTHS) with lots of love, lies, bleeding? (‘Lots of Love-lies-bleeding’ is a plant of the AMARANTHS family),
24 French flower (French flower/river -LOT-) found in delta (Delta) all over the place (= anagram indicator) (Delta = AL-TED) (ALLOTTED) is handed out (ALLOTTED),
25 Bar (BAN-) man (guy) loses unknown quantity (y) (‘guy’ without ‘y’ = -GU-) for opening in (opening ‘In’ = -I) (BANGUI) African capital (BANGUI),
26 The thickest (OBTUSEST) hooligan (yob) loses the head (y) (‘yob’ without ‘y’ = OB-) and takes drugs (-USES-) in race (TT race = -T-T) (OBTUSEST),
27 Greta Garbo dismisses bore (‘Greta Garbo’ dismisses ‘bore’ = grtaga = RAGTAG) as unkempt (RAGTAG).
Down:
1 Reviews (= reversal indicator) Indian music (raga = agar) a couple of times (agar x 2 = AGAR-AGAR), as it’s a cultural phenomenon at The Strand (in seaweed / biological culture = AGAR-AGAR),
2 Shot (PORTRAIT) by Irish beach (Irish ‘beach’ = ‘trá’ = -TRA-) near institute (-I-) in docks (port = POR-T) (PORTRAIT),
3 County (Offaly) is short (y) (‘Offaly’ without ‘y’ = OFFAL) of waste material (OFFAL),
5 Songbird (MOORLAND CHAT) from Othello (MOOR-) and (-AND-) following (position indicator) Lear, the first (‘Lear’ the first = -L-) to speak (CHAT) (MOORLAND CHAT),
6 They’re employed by cleaners (HANGERS-) getting to switch (-ON switch) (HANGERS-ON) with sycophants (HANGERS-ON),
7 Tough old bird (BOILER) produced half a dozen in 11 down (half a dozen of ‘boilermakers’ = BOILER),
8 Those hiding in Bahamas set sights (those hiding in ‘bahamAS SET Sights’ = ASSETS) on the balance sheet (ASSETS)
11 They sell bread (bakers = B-AKERS) around States (= homophone indicator), Greece (‘greece’ = ‘grease’ = OIL-) and Oriental (East = -E-) address (Mr) upsetting (= reverse indicator) (Mr = -RM-) (BOILERMAKERS) those banging out equipment for the house-warmings? (BOILERMAKERS),
15 American (A-) and French men (Messieurs = -MM-) on (-ON-) one (-I-) film location (set) turning up (= reverse indicator) (set = -TES) (AMMONITES) for Jurassic Fossils (AMMONITES),
16 Unable to open up (AIRTIGHT) to couple (pair) losing the head (p) (‘pair’ without ‘p’ = AIR-) with local drunk (local ‘drunk’ = -TIGHT) (AIRTIGHT),
17 Gathering (AMASSING) at start of (‘At’ start = A-) church service (-MASS-) for popular (-IN-) legend (‘leG’ end = -G) (AMASSING),
19 Two graduates (BA+ MA = BAMA-) getting green light (OK) backed (= reverse indicator) (OK = -KO) (BAMAKO) with African capital (Capital of Mali = BAMAKO),
20 Charm (AMULET) broker away from troublemaker (‘broker’ away from ‘troublemaker’ = tulema = AMULET),
23 A (A-) rare group of whales (-GAM-) leading alligator (foremost ‘Alligator’ = -A) (AGAMA) and lizard – in the old-world sense! (Old World lizard = AGAMA).