The incident occurred at the tail end of a skirmish stemming from a hit by Capitals forward Brendan Leipsic. He flattened his opponent behind the net and multiple fights broke out as Chandler Stephenson buried the loose puck to extend Washington's lead to 3-0.
The Ducks were predictably incensed with Hathaway after the game.
"That's about as low as you can dig a peg," Gudbranson told Stephen Whyno of The Associated Press.
Hathaway said the spit was a reaction to a sucker punch thrown by Gudbranson.
"Obviously, first there was a fight and then how I saw it was they had a third man in. I think they had a fourth man in, too," Hathaway said, according to NHL.com's Tom Gulitti. "The refs were trying to break it up and it felt like there was a couple sucker punches thrown and I got one quick and then reacted a little emotionally and unfortunately spit came out of my mouth after I got sucker punched and it went on him."
Six different players were handed penalties amid the chaos, though Hathaway is likely the only one of the bunch facing supplemental discipline from the league.