I'm wondering what this new icon means. The number, border and colors change size and shape between players.
That icon shows a player's Endorsement level, while the colours represent how many endorsements of each kind - Sportsmanship in green, Good Teammate in purple, and Shot Caller in orange - that player has received. You can endorse other players at any time after a quick play or competitive match has ended.
Some arcade game modes also support achievements:
For more information, visit the official website's page on endorsements.