Looks good either way although I'm partial to long hair. But if you dont like it, grow it out again.
A little early but getting to be the time of year when songbirds are establishing or reaffirming their territories. This cardinal, and I would assume it's a male, sees his reflection in the glass and thinks it's another bird invading his turf. He pecks at that "other bird" to make it go away and it pecks right back!
Cardinals, titmice and robins were the species I used to get the most calls about back in the day doung this. Eventually, after a few days or a week or two, they give up because they move into the nest building phase.
There are lots of suggestions about how to discourage them but wHat we advised people to do was smear something on the OUTSIDE of the glass that they cannot see through, such as bon ami, or you can tape some newspaper to cover the glass. It works because the bird thinks it got rid of the intruder and stops trying to chace him away. You leave that up for a couple of weeks and you do it on the outside because if it's inside the bird can still see its reflection/the intruder.