Male Robins tend to be possessive of their territory during mating season. For some, seeing their own reflection in a window is enough to drive them nuts. They go into "attack mode" attempting to drive the intruder away, but, of course they are the intruder, but are incapable of realizing it. The result is a daylong attack of obnoxious intruder. This video is of a few crashes over a week,
For some reason, they do not seem to be hurt by all the crashing.