A fairly typical Rufus mix of anagrams and double and cryptic definitions, with the usual silky-smooth surfaces, mostly straightforward, which is no bad thing at this busy time, with a couple of [for me] less familiar words. Thank you, Rufus.
Definitions are underlined.
1 Knocked about a lot, as veteran campaigners?
IN THE WARS
6 Painter’s material
a painter [line attached to the bow of a boat to tie it up] is made of rope – a trademark nautical reference from Rufus
8 Pulling up and filling up
9 Wild parrot, a bird of prey
anagram [wild] of PARROT
10 Grinds away at university course, say
sounds like [say] Greats, the Oxford University Honour School of Literae Humaniores
11 Remote chance for a sniper?
12 Ancient city‘s role in South Africa
SPARTA [role] in SA [South Africa]
15 Abandon wickedness? Not this woman
SHED [abandon] EVIL [wickedness]
16 Clock at one perhaps? Have a drink
anagram [perhaps?] of CLOCK AT I [one]
19 Gift for producing story book in abbreviated form
TALE [story] NT [abbreviation of New Testament - which, of course, is actually a collection of books and usually clued as such]
21 Try repeatedly to express approval
HEAR [try] repeatedly
22 Gun dog disturbed a mammal
anagram [disturbed] of GUN DOG
24 Staff, say, joining English riding school
MAN [staff] + EG [say] + E [English]
This word seemed familiar [probably from crosswords] when the wordplay unfailingly led to it
25 Graduate as a footballer?
BA [graduate] is half of BAck – this made me smile and is my joint favourite clue
26 Small supports in the river
27 Ships carrying right pennants
STEAMERS [ships] round [carrying] R [right]
1 Put down as late
2 He will have marked cards, of course
cryptic definition, referring to racing cards and race courses
3 Departures could be set about eleven
anagram [could be] of SET round XI [eleven]
4 Guardian supported by American in prayer
ANGEL [Guardian] before [supported by, in a down clue] US [American]
5 Rigid line taken by hospital department
STRING [line] + ENT [hospital department]
6 So “Tripe” is silly retort
anagram [silly] of SO TRIPE – a great surface
7 In favour of moving to get a better job?
PRO [in favour of] MOTION [movement]
13 Walk recollected in Arden poem
anagram [re-collected] od ARDEN POEM
14 Various news areas provide knowledge
anagram [various] of NEWS AREAS
17 We hear officers are at the heart of things
sounds like [we hear] colonels
18 One staggering on all fours?
double / cryptic definition – a lurcher is a type of dog
20 Good characters are, for example, caught in wicked libel
EG [for example] in anagram [wicked] of LIBEL – a great surface and my other joint favourite clue
22 A current coastal issue
23 Cuts with no sound
sounds like NIX [no]