You’re in luck - Blizzard actually [filed for a patent] for the Play of the Game system. In order to obtain a patent on something, the inventor of the invention needs to explain exactly how the invention works. After deciphering most of the legal language, here’s how I understand it works:
First, individual player actions are categorized and assigned scores. Killing an opponent have a higher score than injuring one. Hitting multiple opponents would score higher than hitting a single opponent. Saving an ally from a fatal attack (through healing, shielding, etc.) is more valuable than topping an ally off. Other mode-relevant actions like capturing a point, pushing the payload, or capturing the flag are also scored. Doing something while airborne (e.g. falling, jumping, etc.) or moving at top speed is also granted a point bonus, likely because anything done in the air is cooler. These scores are not completely attributed to the individuals performing them. In order to encourage team play, doing things like supporting a teammate (peeling enemies off, healing, resurrecting, shielding damage, etc.) grants some portion of the score earned to the supporting player in addition to the active player.
Since the Play of the Game clip has a set length of time, the game calculates a running score for all of the action in the game for last X seconds. It also keeps a timestamp for the preceding X seconds that hold the highest overall score so far. That timestamp is for the current Play of the Game. As the running score rises and falls, the current Play of the Game can change. Once the game is over, the game goes back to the time stamp of the highest-scoring X seconds (with a little bit of additional buffer added before and after to make it more cinematic) and packages that into the Play of the Game video from the perspective of the highest-scoring player.
This method also makes it fairly easy to keep running tallies for each player in the game as the match progresses. Each player’s highest-scoring moment then can get packaged as their own personal highlight even if it isn’t the Play of the Game.
Got a burning question you want answered?