|Specsavers County Championship Division One, Cooper Associates County Ground|
|Somerset v Yorkshire, day three|
|Somerset 562-7 dec: Hidreth 166, Trescothick 97, Trego 94; Rashid 4-160|
|Yorkshire 306-9: Lyth 106; Groenewald 3-50, Gregory 2-55|
|Somerset lead by 256 runs|
|Somerset 7 pts, Yorkshire 4 pts|
Somerset's bowlers toppled Yorkshire's middle order to leave the the champions on the brink of following on at Taunton, despite Adam Lyth's century.
The visitors resumed on 127-1 and Lyth reached his ton, before driving Lewis Gregory to first slip for 106.
After tea, Yorkshire lost five wickets for 11 runs as they collapsed to 237-9.
Steven Paterson and Jack Brooks' 69-run last-wicket stand helped the away side to 306-9, still needing another 107 runs to avoid the follow-on.
Lyth's impressive second first-class century of the season included 12 fours and three sixes, but his departure left the visitors struggling.
Yorkshire resumed the final session at 16:45 BST, with 30 overs to play in the day, on 213-4 but Tim Groenewald produced a terrific spell of bowling.
After Gregory had Jack Leaning caught behind and Adil Rashid was run out, Groenewald induced edges from Gary Ballance and Liam Plunkett and bowled Andy Hodd to leave the visitors in shock.
Despite Patterson (32 not out) and Brooks (34 not out) holding off the hosts bowlers for the remainder of the day, Somerset will be looking to push for victory on the final day.