What are the numbers for players?

During a match each hero has the player name above, but for some reason on the left of the name there is a number. It's also on their jersey, and shows up every time they highlight that player. What is the point of the number? I'm pretty sure that it's just copying traditional sports so it's easier to identify players but in the context of Overwatch it just seems pointless. Also some players have the same number (i.e. Mano and Tobi both have number 7). It's just kinda weird and I'm wondering if there's another reason why it's there.

It's to make sure Coolmatt can still have 69 on him, no other reason

It makes little to no sense, I think they want numbers so they can say 'Look, we're like real sports', but in reality they serve no functional purpose.

Unlike these other British nonces I like the numbers. Yeah it's a bit pointless but it adds a bit of personality to the players, usually each player has a reason behind why they picked their number. I'm all for a little extra added bonus

PapalWizard [#2]

It's to make sure Coolmatt can still have 69 on him, no other reason

Bingo!

Wombat [#4]

Unlike these other British nonces I like the numbers. Yeah it's a bit pointless but it adds a bit of personality to the players, usually each player has a reason behind why they picked their number. I'm all for a little extra added bonus

Then it makes sense Fleta has number one

4 4 S4

In a league with more than 100 players (iirc) there are bound to be some repeating numbers. They also serve the purpose of allowing players to keep the numbers they had in their usernames as otherwise they were forced to remove them.

Pixelfish [#7]

4 4 S4

S4Head