ACROSS
1. "BANNED" = BAND <gang>
4. STAR PUT* + S = START-UPS <new companies>
8. ABS + TRACTION = ABSTRACTION <the general idea>
9. <seat> THRONE = "THROWN"
10. (...l)E CHO(i...) = ECHO <E>
14. <injury's result> SCAR = ⭯CARS⭯
15. <bridge> RIALTO = _RI_ + ALTO
18. <professional footballers> LIVERPOOL FC = (PELVIC FLOOR)*
19. BALLSY* + US = SYLLABUS <curriculum>
20. "SOW LOW" = SOLO <music without accompaniment>

DOWN
2. A PATHETIC ALLY = APATHETICALLY <showing no enthusiasm>
3. ←(...g)O CSI D(e...)← = DISCO <nightclub>
4. <inspector> SURVEYOR = V inside SURE Y O_R
5. <principal> ARCH <curved structure in building>
6. T_R_I_ + MERE* = TRIREME <rowboat>
7. (...i)PANT HEIST I CAL(l...) = PANTHEISTICAL <keeping all idols>
11. <fake> SPURIOUS = SPUR IOUS
13. ←RA← RIVAL = ARRIVAL <showing up>
16. ←SALT A← = ATLAS <map collection>
17. <unimaginative> DRAB = ←BARD←