Special instructions today were "NB - the four marked clues are all 1-across 21-down [sporting cliches]". A little tricky, but not insurmountable once I got back on DA's wavelength. Not completely sure about all of my parses: the "ATA" in 10A feels a bit flimsy; there's no insertion indicator in 24A; I also don't see much more than a straight definition in 16D. Otherwise not too bad, and the theme was fun at least!

Across

1

Fair laundry job absorbs last of soap (8)
SPORTING — SORTING (laundry job) containing P (last letter of soap)

10

• (& 19-down) Steadily secured frail-sounding attack, largely to yield in return (3,4,2,1,4)
  ONE WEEK AT A TIME — homophone of WON (secured) WEEK (frail), ATA (most of attack?), reversal (in return) of EMIT (to yield)

11

Belabours wretched orphans (5,2)
HARPS ON — anagram (wretched) of ORPHANS

13

Heard Jagger’s over confusion (3-2)
MIX-UP — homophone of MICK'S (Jagger's), UP (over)

14

Most reserved bid, conceding nothing to pro vote (6)
SHYEST — SHoT (bid) with o (nothing) -> YES (pro vote)

15

Joins conversation to discuss method? Wrong (6,2)
WEIGHS IN — homophone of WAYS (method), SIN (wrong)

18

• (& 5-across) Tender Darwin fool baked French bread (2,1,5,2,4)
  IN A WORLD OF PAIN — anagram (baked) of DARWIN FOOL, PAIN (French bread)

20

Flashes terrify current seat of aggression (6)
MOSCOW — MOS (flashes) COW (terrify)

24

Swell once insane at orgy (5)
NEATO — hidden in insaNE AT Orgy

26

1-across headache needs regular wellness, cycling, jogging, tonic? (9)
SELECTION — anagram (cycling) of ELES (even letters of wellness), anagram (jogging) of TONIC

27

Bouncer occasionally the ultimate winner (7)
EVICTOR — E (last letter of the) VICTOR (winner)

28

Jazz's Louis wearing mackintosh to escape family (7)
SATCHMO — anagram (wearing) of MACkinTOSH without kin (family)

29

Every 168 hours, overturned leader in 14-across style? (6)
MEEKLY- — wEEKLY (every 168 hours) w -> M (overturned leader)

30

Raves wildly, then attends functions (8)
ENTHUSES — anagram (wildly) of THEN, USES (functions)

Down

1

Campaign features hard work and interminable kisses on the rear (7)
SLOGANS — SLOG (hard work) ANd (without last letter) S (last letter of kisses)

2

When public can visit to spend May off their faces? (4,3)
OPEN DAY — tO sPEND mAY, each without first letter

3

• (& 18-down) Asinine theorem? It applied to groupthink (5,2,2,1,2,4)
  THERE IS NO I IN TEAM — anagram (applied) of ASININE THEOREM IT

4

Share index that’s related to gathering $1000 up (6)
NIKKEI — reversal (up) of IE (that's) KIN (related to) containing K ($1000)

6

Chatroom promoting English filler? (5)
FORUM — FOR (promoting) UM (English filler)

7

• (& 12-across) Send sex assent via mobile, all over the shop (2,5,3,6)
  AT SIXES AND SEVENS — anagram (mobile) of SEND SEX ASSENT VIA

8

Square peg a 1-across target (7)
NINEPIN — NINE (square) PIN (peg)

9

Dodgy lawyer arranged 14-across second trial (7)
SHYSTER- — anagram (arranged) of SHYEST (14-across) R (second letter of trial)

16

1-across triumph by keeper? (4,5)
GOOD CATCH — cryptic def.

17

The Spanish cut pickle ending (7)
CLOSURE — CURE (pickle) containing LOS (the Spanish)

21

Seals out north - they’re weary (7)
CLICHES — CLInCHES (seals) without n (north)

22

Chances Microsoft program (7)
WINDOWS — double def.

23

Girl also in strife (6)
ALISON — anagram (strife) of ALSO IN

25

Freezing almost unlikely in Base 8 (5)
OCTAL — OC (freezing) TALl (unlikely, without last letter)