A decent coffee-time solve with a couple of talking points.
There are no rules about the balance of clue-types. Indeed, an preponderance of one type may produce its own misdirection, as in ‘he wouldn’t do that again, would he?’. But there are three very similar clues close together today. Perhaps it’s just Slormgorm keeping us on our toes…

Across | ||
1 | BACKING | Support Britain wanting rid of leader (7) |
B[ritain] + (L)ACKING sans 1st letter. | ||
5 | BRAMBLE | Chatter pointlessly on black Blackberry (7) |
B[lack] + RAMBLE (‘chatter pointlessly’). | ||
9 | LINES | Punishment for a schoolboy error? (5) |
Not-so cryptic whole clue definition. | ||
10 | RESTRAINT | Reserve shower possibly during leisure time (9) |
REST (‘leisure’) + RAIN (‘shower possibly’) + T[ime]. | ||
11 | IN THE MAIN | A hint men and I must change for the most part (2,3,4) |
Anagram (‘must change’) of A HINT MEN, I. | ||
12 | CHINA | Church popular with a friend in the East End (5) |
CH[urch] + IN (‘popular’) + A, ‘China plate’ being Cockney rhyming slang for ‘mate’. | ||
13 | HABIT | Rather put on hot clothes (5) |
H[ot] + A BIT (‘rather’). | ||
15 | DEODORANT | Don’t adore criminal that smells nice (9) |
Anagram (‘criminal’) of DONT ADORE. | ||
18 | OVERTIRED | Do back detaining bad riveter in need of the sack (9) |
DO reversed around anagram (‘bad’) of RIVETER, plus cryptic definition. | ||
19 | STOIC | Philosophical type objects to ice-cream sandwiches (5) |
Inclusion in ‘objectS TO ICe-cream’. | ||
21 | TRIAL | Test case? (5) |
Double definition. | ||
23 | BANDWAGON | Successful movement of a tour bus, perhaps (9) |
Cryptic alternative definition. | ||
25 | OVER AGAIN | Romeo Vera gainfully cuddles another time (4,5) |
Inclusion in ‘romeO VERA GAINfully’. | ||
26 | OLIVE | Piece of oily and, on the turn, bad fruit (5) |
‘O’ (‘piece of Oily’) + reversal of EVIL (‘bad’). | ||
27 | RELIEVE | Assume responsibility of another’s Duty Free (7) |
Double definition. | ||
28 | ELEMENT | As an example, one might say Krypton Factor (7) |
And another. Both are remarkably (& perfectly fairly) unbalanced. But adjacent clues…? And see 2d. | ||
Down | ||
1 | BALDISH | Being somewhat less shocked than before?! (7) |
Jocular whole-clue def, ‘shocked’ of course being crossword-ese for ‘having [shocks of] hair’. | ||
2 | CONSTABLE | Person in the employ of the police artist (9) |
And a 3rd unevenly split DD. | ||
3 | ISSUE | I bring legal proceedings about small matter (5) |
I SUE around S[mall]. | ||
4 | GERMANDER | Plant men regard in a state of excitement (9) |
Anagram (‘in a state of excitement’) of MEN REGARD. | ||
5 | BISON | One’s to tuck into good French beef alternative (5) |
1’S in BON (‘good’ in French). | ||
6 | ATROCIOUS | Sadly, our old cat is horrible (9) |
Anagram (‘sadly’) of OUR O[ld] CAT IS. | ||
7 | BLINI | Pancake day is shunned by visually impaired institute (5) |
D[ay] removed from BLINd + I[nstitute]. | ||
8 | EXTRACT | Pull out more conservative trunks at the front (7) |
EXTRA (‘more’) + C[onservative] + 1st letter of Trunks. | ||
14 | TITILLATE | Tickle a little drunk with it (9) |
Anagram (‘drunk’) of A LITTLE, IT. | ||
16 | ORDINANCE | Old Republican steps, perhaps to secure home rule (9) |
O[ld] + R[epublican] + DANCE (‘steps’) surround IN (‘home’). | ||
17 | ALONGSIDE | Possibly touching description of a hypotenuse? (9) |
The hypotenuse of a right-angled triangle is perforce ‘a long side’. I recall some sort of rule about it. | ||
18 | OUTDOOR | Expose men holding party in the open air (7) |
OUT (to ‘expose’) + O[ther] R[anks] (= ‘men’) surround DO (‘party’). | ||
20 | CONTEST | Dispute examination of a prisoner? (7) |
‘CON[vict] TEST’. | ||
22 | IDEAL | I do business with another model (5) |
I + DEAL (‘do business with another’). | ||
23 | BRAVE | Endure first part of bachelor party (5) |
B[achelor] + RAVE (‘party’). I think deleting ‘first part of’ could be an improvement. | ||
24 | WHOLE | Undamaged, but unattractive place reportedly (5) |
Homophone (‘reportedly’) of HOLE (an ‘unattractive place’). |
*anagram
Thanks to Slormgorm and Grant. If my schoolboy maths lessons serve me correctly the rule you refer to @ 17d is “The square of the side of the hypotenuse is equal to the sum of the squares of the other two sides”
To Niltac:
That’ll teach me not be facetious.
Thanks Slormgorm and Grant
Seemed to struggle through what was a fairly straightforward solve here. Needed a second session to finish off the bottom of it.
Apart from the three near consecutive double definitions, most of the down clues appeared to be charades with a bit of a tricky one about the rule. A couple of cleverly disguised hidden answers in the across clues.
Finished in the SW corner with ORDINANCE, TITILLATE and RELIEVE the last few in.
Thinking “less shocked” = “more confident”, I had “bullish” for 1 down.
Thanks Grant and Slormgorm.