Is the L safe at night?

At one time, the neighborhood was dangerous.

It's actually reasonably safe there nowadays. The United Center is near a bunch of hospitals and the University of IL Chicago campus. Just stay with the crowds on Damen Avenue after the game, and you will probably notice that several hundred fans will be walking to the Blue Line.

The very first time I went to Chicago I went to a show that ended close to midnight. I had the exact same worries as you and had planned for a cab back to my hostel. Turns out I had nothing to worry about because the L stations are very well-lit and there were a LOT of people riding it that time at night, including many people who were leaving the show, same as me. I felt the "safety in numbers".

My guess is that if you're leaving a Blackhawks game there'll be a LOT of Blackhawks fans who will be riding the train at the same time as you.

That being said you should have cab fare at the ready just in case things don't feel right.

It is absolutely fine and safe. Seriously.

You might also want to consider taking the bus right on Madison. An express bus runs after events to the loop. It can get crowded, but it's quick and convenient.

It's safe unless you wave around your expensive jewelry, and keep displaying your expensive cell phone. Be cautious after you get off the train.

Seriously? You'll be with all the other fans leaving the game. Thousands of people take the L every day- do you think they would if they were going to get robbed/stabbed/shot?

if you are very big, no problem. if you are kind of big and kind of drunk, lots of problems.