Chris Noth had several reasons for leaving Law & Order. Noth played Detective Mike Logan in the series’ early years. Logan was dedicated to the job, but could be a hothead, which sometimes got him into trouble. He beat up a suspect who gunned down his first partner during the season 2 opening, which was one of Law & Order‘s best episodes. Eventually, Logan was transferred to Staten Island Domestic Disputes after punching a homophobic politician, which was supposed to be the end of his career
https://screenrant.com/law-and-order-chris-noth-mike-logan-exit-reason/