While trying to prevent Seahawks wide receiver David Moore from making a catch, Thomas launched into Moore and made helmet-on-helmet contact with him just after the ball dropped in front of him. Moore was left shaken up on the play and the Colts were also penalized 15 yards.
Thomas is the first player to be ejected under the NFL's expanded use of helmet rules, that allows officials to eject players in violation.
Under the amended rules, any player who lowers his helmet to establish a linear body posture prior to initiating and making contact with the helmet and is unobstructed in his path to the opponent is subject to ejection.
"That was very disappointing. I'm very disappointed," Colts coach Frank Reich said after the team's 19-17 win. "We don't teach that. That was a good call, that was the appropriate call, he should have been ejected. ... That could have been avoided, should have been avoided, and the referees did the right thing."