Solution to 17D has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
1 Instant a sport organization becomes an old beast (11) TRICERATOPS {TRICE}{A+SPORT}*
10 His hold on old country mountain ranges (9) HIMALAYAS {HI{MALAYA}S}
12 Burn one, fifty gone! (5) SINGE SINGlE
13 Essentially need to keep watch over the recluse (7) EREMITE {nE{TIMER<=}Ed}
15 Criticize the bid (4) SLAM [DD]
18 Extremely stressful work on sewage water (4) SLOP {St...uL}{OP}
20 Old sea farers had six cards... (7) VIKINGS {VI}{KINGS}
23 ...others got one finally to turn off and on again (5) RESET {RES{onE}T}
24 Usual sides go into cheer a natural reproductive process (9) OVULATION {OV{UsuaL}ATION}
26 Girl — one caught in the blaze, perhaps (9) ELIZABETH {1} in {THE+BLAZE}*
27 Reading about most cruel attack (5) STORM {STO{R}M*}
28 Toiled regularly for a match (3) TIE ToIlEd
29 Mere startup making hearing aids (3,8) EAR TRUMPETS*
DOWN
1 Adapted or followed around? (8) TAILORED {TAIL{OR}ED}
3 Smallest error while handling a chemical (5) ESTER [T]
4 Two articles allowed inside "Sportstar" (7) ATHLETE {A}{TH{LET}E}
5 Average return with top money invested — is it slow assimilation? (7) OSMOSIS {SO{Mo..y}SO}<={IS}<=
6 What you need to sell? Pursue drinking few beers (5,4) SALES TALK {S{ALES}TALK}
7 Further pledge, having short sight (6) BEYOND {B{EYe}OND}
8 Writer places America between one and ten (6) AUSTEN {A}{US}{TEN}
14 All I see at random, showing nervousness (3,2,4) ILL AT EASE*
16 Medicine against love (8) ANTIDOTE {ANTI}{DOTE}
17 Must rise, morning is for those monster waves (8) ?S?N?M?S ()
19 First one in port (7) PIONEER {PI{ONE}ER}
20 Told to guarantee her ticket (7) VOUCHER {VOUCH}{HER}
21 Zealous with my time (6) ARDENT {ARDEN}{T}
22 Endeavour of a father to keep quiet (6) ASPIRE {A}{S{P}IRE}
25 A service set up in state (5) ASSAM {A}{MASS<=}
Reference List
Right = R, Victory = V, Fifty = L, Reading = R, Time = T, Quiet = P