This is known as a pretextual stop and these have been held to be legal by SCOTUS for decades. Whren v. US (1996). My daughter was pulled over twice when she was high school. Once for a license plate light out and once for speeding 1 mph over. The 1 over she was leaving a party and they where watching for underage drinking. The license plate light was because she looked really young and it was past midnight which was when the Cinderella licenses were not valid. She had recently turned 18 so she was OK. Most parents would never have known their kid got pulled over. Both times she was stopped in Oldham County by OCSO Deputies, my brothers in arms. It’s so much easier if she would tell me. I didn’t make a big deal of either since she really wasn’t doing anything wrong, but she knew I knew. Don;t you know, dads know everything!