The Mariners announced that Paxton left with lower back stiffness, according to Tim Brown of Yahoo Sports.
Paxton was roughed up by the Angels during his brief outing. In only 2/3 of an inning, he allowed home runs to David Fletcher and Albert Pujols, while also displaying a slight decrease in velocity. Following Pujols' homer, Paxton was visited on the mound by Seattle's training staff and was then lifted from the game.
The 29-year-old Canadian is enjoying an excellent season and came into Thursday's start sporting a 3.49 ERA, 1.07 WHIP, and 154 strikeouts while leading the league in shutouts and complete games. In May, he threw a no-hitter against the Toronto Blue Jays.