punctuation after speech tags

Do I need a comma after the speech tag?

"Tell me about it," he said, as he climbed the stairs.

"Come here," Danny repeated, when his wife didn’t move.

I use them if there’s a present participle after:

"Why won’t you let me pass?" he yelled, punching his math teacher in the face.

But are there more rules for when I must use them or when I shouldn’t