Across:
8 The butterfly (swimming STROKE) found in 15 across, for instance (‘Australian crawl’ = STROKE),
9 Those taking a dip for 15 across (SWIMMERS taking a dip for ‘Australian crawl’) and fish (SWIMMERS),
10 Poles (BARS) on both sides of baseball players (on both sides of ‘BAseball playeRS’ = BARS),
11 This will lead you down the garden path (RED HERRING) to shady type (RED) similar to one of those in 9 across (HERRING is similar to one of the ‘swimmers’) (RED HERRING),
12 Catches sight of (ESPIES) banks of Eccles cakes (banks of ‘Eccles cakeS’ = ES-) in the bakery’s window (-PIES) (ESPIES),
14 Ultimate performance (SWAN SONG) of number synonymous with The Children of Lir (number/song synonymous with The Children of Lir = SWAN SONG),
15 Overseas stroke (AUSTRALIAN CRAWL) produced by Darwinian figure perhaps (person from Darwin, Australia, perhaps = AUSTRALIAN) on most of those in 19 down (most of ‘crawls’ = CRAWL) (AUSTRALIAN CRAWL),
18 Old (-O-) play- (= anagram indicator) -actor (actor = TOR CA-) is consumed by Mr (Mr = M-R) (MOTOR CAR) T, the model? (model T = MOTOR CAR),
20 Detective (-PI-) in Mayo (Mayo) hampered (= anagram indicator) (Mayo = MYO-A) (MYOPIA) by lack of imagination (lack of imagination/foresight = MYOPIA),
22 Spike (PIN-) approaches English (-E-) Market (MART-) for a fair amount of (half of) cattle (half of ‘oxEN’ = -EN) (PINE MARTEN) and an animal similar to a weasel (PINE MARTEN),
24 A (A-) course (-WAY) (AWAY) for getting out of the house (AWAY),
25 A (A-) Trim (r) storyteller (liar) (‘liar’ without ‘r’ = -LIA) is following (= position indicator) military alliance (-NATO-) (ANATOLIA) in Turkey (ANATOLIA),
26 Make an appearance? (TURN UP) That’s one for the books, surprisingly! (a TURN-UP for the books).
Down:
1 Holds up (STEALS) late (late = -TEAL-) shift (= anagram indicator) in boat (SS = S-S) (STEALS),
2 The common sense (NOUS) to set up (= reverse indicator) paper (Sun = N-US) around Oxford (-O-) (NOUS),
3 State (State of NEBRASKA) of new (N-) engineer (-E-) – a supporter of female (BRA-) music synonymous with Jamaica (SKA music) (NEBRASKA),
4 Bruised, missing rib (‘bruised’ missing ‘rib’ = used = USED) and worn out (USED),
5 The pictures (CINEMA) of medicine man taking off denim (‘medicine man’ taking off ‘denim’ = iceman = CINEMA),
6 Producer (IMPRESARIO) marries (marries) model (= anagram indicator) (marries = IM-RESAR-) overlooking park (-P-) for second time (second ‘tIme’ = -I-) near Ring (-O) (IMPRESARIO),
7 What’s more (-AND), it’s new (N-) in beer (brew = BR- -EW) (BRAND NEW) that’s completely fresh (BRAND NEW),
13 Investor (investor) organisation (= anagram indicator) (investor = INTROVE-S) welcomes retweet (-RT-) (INTROVERTS) from those who are withdrawn (INTROVERTS),
14 School (S-) and institute (-I-) in Kildare (KE = -K-E-) is right (-R) (SKIER) for one with a sporting career that’s going downhill (SKIER),
16 Milne is out of emulsion paint (‘Milne’ is out of ‘emulsion paint = usopaint = UTOPIANS), painting the idealistic picture perhaps (UTOPIANS),
17 Mention a (mention a) play (= anagram indicator) (mention a = NOMINATE) to recommend (NOMINATE),
19 Turns up (= reverse indicator) barman (Senior Counsel = SC = C-S) admits 50 (Roman 50 = -L-) to combat (war = -RAW-) (CRAWLS) creeps (CRAWLS),
21 Legendary victim (victim from legend = ICARUS) The Sun destroyed (ICARUS flew too close to the sun against his father’s advice),
23 Cook (steam) needs no introduction (s) (‘steam’ without ‘s’ = TEAM) to the saffrons of Armagh, for instance? (‘The Saffrons’ = nickname of the Armagh TEAM),
24 Is open (AIRY) for leprechaun (fairy) heading off (f) (‘fairy’ without ‘f’ = AIRY).