Josh Thomas, 21, continued his impressive season for Somerset, hitting his third century of the season against Leicestershire. The Division One leaders finished day one at Uptonsteel Grace Road on 354-9, with Thomas contributing 100 runs and sharing a 181-run opening stand with Tom Lammonby, who scored 74.
Despite a session lost to weather, Leicestershire fought back to claim full bowling bonus points. Nathan Gilchrist, on loan from Warwickshire, took 2-65, while James Rew added an unbeaten 52 for Somerset.
Leicestershire, currently in the bottom two, learned before play that they have been charged with breaching ECB regulations over a sub-standard pitch. They face losing 19 points from a previous win if their appeal fails, which could make avoiding relegation from Division One extremely difficult with only two rounds remaining after this match.
Somerset, by contrast, is seeking their first-ever red-ball competition title, having moved into the top spot last week.