Overwatch players know to avoid tunnels if there is an enemy Junkrat or Pharah around, as explosive damage is a great way to choke a team out of a narrow corridor. This Wrecking Ball has his own tunnel moment and makes sure no enemy gets through alive.
In the clip, posted to the Overwatch subreddit Monday by u/Hawaiian_Shirt12, the enemy team decides to take a shortcut through the tunnel, seeing as they almost have the payload at the checkpoint. Even though they are facing a team with a Pharah, they figured that Lucio's speed boost and Sigma's shield and Kinetic Grasp would be enough to get through. Wrecking Ball finds a quick way to wipe them out.
Wrecking Ball was awarded play of the game with this perfect placement of his Minefield Ultimate. He drops the mines behind the enemy team, near their side of the tunnel entrance. It's always optimal to put mines behind the enemy, as their first instinct is typically to back up. He also blocks the entrance which ensures any healer trying to get in or out will be eliminated. The mines get an immediate quad kill and the lone enemy Sigma succumbs to the mines seconds later when backing out.