Across:
1 Game (TENNIS) to open 18 across (open ‘tennis racket’ = TENNIS),
4 The actor (the actor = THEOCRAT) playing (= anagram indicator) one of The Two Popes (THEOCRAT),
9 Snippet (LOCK-) from Alien (-ET) (LOCKET) – a reminder of a much-loved one, just in case (LOCKET case),
10 Club (bat = B- -AT) admits shortfall (-LACK) relates to initial costs (initial ‘Costs’ = C-) (BLACK CAT) – is there something familiar about that? (BLACK CAT of a witch is called a ‘familiar’),
12 Begin work (GET A START) to hire (GET) American (A) celebrity (STAR-) for lead in Transformers (for lead in ‘Transformers’ = -T) (GET A START),
13 Host is not part of threesome (‘host’ is not part of ‘threesome’ = reeme = EMEER) with unconventional Arab leader? (unconventional ‘EMEER’ can be spelt emir / amir / ameer),
14 Sporting facilities (TENNIS COURTS) produced by those in 1 across (‘tennis’ = TENNIS) and 20 down (‘courts’ = COURTS) (TENNIS COURTS),
18 Thuggish leader (‘Thuggish’ leader = T-) in Clare (-ENNIS) linked to shady business (RACKET) (TENNIS RACKET) is subject of underhand tactics in court (TENNIS RACKET),
21 Concealed by Pietro Badoglio (concealed by ‘pieTRO BAdoglio’ = troba = ABORT) going back (= reversal indicator) (troba = ABORT) to cancel launch (ABORT),
22 Brought joy to (GLADDENED) young man (-LAD-) getting to study (-DEN-) in, for example, (e.g.) flipping (= reversal indicator) (e.g. = G-E-) Dublin (-D) (GLADDENED),
24 Cover again (RERECORD) a fair amount of (half of) study (half of ‘REad’ = RE) for Spud (spud/potato = -RECORD) (RERECORD),
25 Book dealers asked out (‘book dealers’ ‘asked’ out/without ‘asked’ = booler = BOLERO) to dance in Madrid (BOLERO),
26 Too wound up (RESTLESS) to relax (REST-) on the foreign (the = -LE-) ship (-SS) (RESTLESS),
27 Slips (SLIDES) in playground (SLIDES).
Down:
1 Where one is charged for driving on course (TOLLGATE) with Count? (TOLL-) Expect drama here! (-GATE Theatre) (TOLLGATE),
2 Notice in (notice in = NICOTINE) complex (= anagram indicator) doesn’t do health any good (NICOTINE),
3 First mate cuts raft (‘first mate’ cuts ‘raft’ = ismte = ITEMS) with a number of objects (ITEMS),
5 Ruth’s (ruths) novel (= anagram indicator) (ruths = THURS-) set during Christmas (HOLY -DAY) (HOLY THURSDAY) and just before Easter (HOLY THURSDAY),
6 Wild (= anagram indicator) roar (roar = OR-RA) over casket (-CHEST-) (ORCHESTRA) produced by one with a job down in pit? (ORCHESTRA),
7 Noise (RACKET) produced by half of those in 18 across (half of those in ‘tennis racket’ = RACKET),
8 Trout (trout) swimming (= anagram indicator) (trout = TUTOR-) ahead of salmon (ahead of ‘Salmon’ = -S) (TUTORS) in school (TUTORS),
11 Stepping out (DANCING) with young ladies (GIRLS) (DANCING GIRLS) from the Moulin Rouge (DANCING GIRLS),
15 Citadel in (citadel in) ruin (= anagram indicator) (citadel in = IDENTICAL) is the very same (IDENTICAL),
16 Perceived as aggressive (SKINHEAD) and depressed (S-AD) over family (-KIN-) on heroin (-H-) and ecstasy (-E-) (SKINHEAD),
17 Most of (y) the analysis (‘study’ without ‘y’ = STUD-) on promissory notes (IOUs = -IOUS) (STUDIOUS) is academic (STUDIOUS),
19 It’s more reasonable (FAIRER) to take tons out of rainforest (take ‘tons’ out of ‘rainforest’ = raifre = FAIRER),
20 Woos (COURTS) Simon away from consortiums (‘Simon’ away from ‘consortiums’ = cortus = COURTS),
23 Amusing (DROLL) retiring (= reversal indicator) characters in small order (characters in ‘smaLL ORDer’ = llord = DROLL).