To immobilize something, usually a vehicle, by placing obstacles, usually other vehicles, obstructing the free movement
If you are boxed in, you are unable to move from a particular place because you are surrounded by other people or cars. Armstrong was boxed in with 300 metres to go The black cabs cut in front of them, trying to box them in. = hem in
If something boxes you in, it puts you in a situation where you have very little choice about what you can do. Part of winning a mandate is having clear goals and not boxing yourself in We are not trying to box anybody in, we are trying to find a satisfactory way forward. + boxed in boxed in The Chancellor is boxed in by inflation targets and sterling