Solution to 20D has been deliberately left unsolved and is to be answered 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 Dash after catching ball and raise cap (5,3) ROUND OFF {R{O}UN}{DOFF}
11 Overeat and turn green after drinking spirit (7) ENGORGE {EN{GO}RGE*}
12 Turned plump in a posh Pacific atoll (5) ATAFU {A}{FAT<=}{U}
13 Man running bare in the open near this place (9) HEREABOUT {HE}{BARE*}{OUT}
14 Quiet! Trooper has distracted marksman (12) SHARPSHOOTER {SH}{TROOPER+HAS}*
18 Perhaps horse might start to accelerate on time in last stretch of racecourse (4,8) HOME STRAIGHT {HORSE+MIGHT+Ac...e}*{T}
21 Obstruction in middle of duct, colon is twisted (9) OCCLUSION {dUCt+COLON+IS}*
23 Master avoids method acting, performs Shakespeare-style (5) DOETH mETHOD*
24 Crisp tale about Irish revolutionary (7) FRIABLE {F{IR<=}ABLE}
25 Queen consort of Jordan welcomed by popular Middle Easterner (7) IRANIAN {I{RANIA}N}
DOWN
1 Tribal gangster chasing vehicle around island (6) RACIAL {AL}<=>{CAR<=} over {I}
2 Synthetic chemical compound contains nitrogen and trace of lithium (6) UNREAL {U{N}REA}{Li...m}
3 Desires to have fun essentially after young socialite seduces (9) DEBAUCHES {A{fUn}CHES}<=>{DEB}
4 Silly exploit by that woman cavorting bare in department (7-7) FEATHER BRAINED {FEAT}{HER}{BARE+IN}*{D}
7 Flavoured wine with exceptionally trimmed chops (8) VERMOUTH {VERy}{MOUTH}
8 See 16
9 Medical expert's so cute - intern is aroused (14) NEUROSCIENTIST*
17 Slapping leader after atrocious scam (8) SMACKING {KING}<=>{SCAM}*
19 Customer in outlet checking a fine woollen yarn (6) MERINO [T]
20 Group eating hot starter of eggs and beef (6) ?H?N?E ()Addendum - WHINGE {W{H}ING}{Eggs} - See comments)
Reference List
Ecstasy = E, Spirit = GO, Posh = U, Quiet = SH, Time = T, Master = M, Popular = IN, Good = G, Amateur = A, Gangster = AL(Capone), Island = I, Young socialite = DEB, Department = D, Island = I, Old = O, Hot = H, Director = D