Billy Root led the way for Glamorgan against his native Yorkshire with 51, but the visitors slipped to 109-4 on a rain-hit first day at Headingley.
Root was dropped at slip by his brother Joe, with the England batter playing his fourth Championship match of the season alongside international team-mate Harry Brook.
Yorkshire claimed two more wickets in a late 30-minute session under the lights after a long delay.
Rain had prevented any play between 13:45 and 17:30 BST.
The game is being played on the same pitch as Yorkshire’s last match against Derbyshire, which finished just four days before.
Glamorgan won the toss for the first time this season and chose to bat despite the overcast weather, given the chances of the pitch being very worn by the fourth innings.
Yorkshire included both specialist spinners, Dan Moriarty and Dom Bess, while Glamorgan added Tom Bevan to their range of back-up spinners to Mason Crane.
Eddie Byrom, returning to the team after a pre-season injury, was trapped lbw by Ben Coad for nine and the seamer also found the edge of Billy Root’s bat only to see Joe shell the difficult slip catch.
Moriarty was on for the tenth over of the game and spun one sharply out of the foot-marks past Root, but he and Sam Northeast looked fairly untroubled for most of their stand of 74.
Root nailed a reverse-sweep and a slog-sweep off Moriarty as he reached 50 off 88 balls, but survived a couple of leg-before shouts in the last over of the first session, before being given out caught at short-leg off the final ball.
His innings followed an unbeaten half-century on his last visit to Headingley and a century on the ground in 2021.
The rain arrived just an over after lunch, but the umpires took the players back out in the evening gloom under the floodlights and Yorkshire struck in unusual fashion as Northeast was run out for 29 at the non-striker’s end, with Matthew Fisher getting a finger to Kiran Carlson’s straight drive.
In murky conditions, Yorkshire had to switch to spin bowling to stay on and they benefitted from that, as Carlson, on three, dragged Dom Bess’s first ball back to the bowler.
Colin Ingram and Chris Cooke survived until the umpires finally decided the light was too bad to continue at 18:00 BST, but Yorkshire had already made the most of their late chance.
