Glamorgan batsman Billy Root has been immediately suspended from bowling in county cricket because of an illegal action, the England and Wales Cricket Board has announced.
The younger brother of England Test captain Joe, Root's part-time off-breaks were subjected to an independent assessment.
The review concluded that Root's action "displayed elbow extension in excess of the permitted 15 degrees".
Root, formerly of Nottinghamshire, has therefore been banned from bowling until "such time he has submitted a fresh independent assessment in which it is concluded that he has remedied his action".
Root responded to the news of his suspension by hitting a half century as Glamorgan closed on 214 for four in reply to Derbyshire's 378.
Charlie Hemphrey made 75, his highest first-class score for Glamorgan, who had earlier been frustrated by Anuj Dal's maiden 50, which helped Derbyshire secure a fourth batting point.
Glamorgan would have expected to keep Derbyshire below 350 after Lukas Carey, who claimed a career-best four for 61, struck three times with the second new ball, only for Dal and Ravi Rampaul to add 50 for the last wicket.
Daniel Douthwaite claimed his second championship wicket when Matt Critchley steered him to second slip before Carey brought one back to bowl Alex Hughes off a glove.
Logan Van Beek was beaten by a full length ball and, when Tony Palladino skied a pull to deep midwicket, a fourth batting point looked unlikely at 328 for 9.
But Dal played impressively after being clattered on the helmet, and three fours from a Douthwaite over took the home side to 350 and some uncomplicated blows from Rampaul added to Glamorgan's frustration.
Dal was finally bowled by Michael Hogan but he had given Derbyshire the chance to put Glamorgan under pressure if they could take early wickets.
The first target for the visitors was 229 to avoid following-on and Nick Selman and Hemphrey were made to work hard by accurate bowling combined with some hostility from Van Beek.
Derbyshire's discipline and patience was rewarded when Selman was dismissed by Palladino and, although Marnus Labuschagne hit Rampaul for six after tea, he was lbw offering no shot in his next over.
Luis Reece was getting the ball to swing and, despite David Lloyd twice driving him through the covers for four, the Glamorgan captain got a leading edge to point as he aimed to play through midwicket.
But Hemphrey was showing the application required and reached his third consecutive championship 50 as he and Root dug in.
Root survived a sharp chance to second slip off Hughes on 16 and he made the most of his reprieve by cover driving the all-rounder for three fours in an over on his way to a 61 ball 50.
Hemphrey resisted until he was lbw to a full-length ball from Van Beek, but Root was unbeaten on 53 at the close.