Image: By David Shankbone (David Shankbone) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
Okay so there's a little more to it than the headline suggests. He was stopped by police for riding the wrong way, but then argued with the cop which is what actually got him arrested. He was issued two citations one for a traffic violations and the other for disorderly conduct.
The incident happened around 9:15am our time. Baldwin was riding the wrong way on 5th Ave in Manhattan and when stopped by police he became belligerent when he couldn't produce proper identification. He was arrested and released before 11am our time.