counter-strike-global-offensive
When playing competitive mode in CS GO, at the end of a round the scoreboard is shown and it takes sometimes up to 30 seconds for the match to actually finish and go back to the menu.
Can I safely disconnect during this event or will I suffer a match making penalty?
The ban systems works as follows:
1st infraction: 30 min.
2nd infraction: 2 hours.
3rd infraction: 24 hours
4th infraction: 7 days
Any one of these infractions get reset after 7 days.
How the banning system works (To the extent of my knowledge):
1. Dealing 80/90+ damage to a teammate at start of game will be instant ban.
2. Doing 400+ of damage to teammate(s) over the period of the whole game can get you banned. (You usually get a warning telling you that you have done a lot of damage and the next time you attack a friendly you will be kicked)
3. Killing 3 teammates
How you got kicked and he didn't: He didn't get kicked purely because it wasn't at the start of the game and in spawn. When it's like that the game knows that there are enemies around and sometimes that you are likely to either accidentally attack your team mate or maybe even kill him. For this they make exceptions. However if you were to do it as a continuous burst of fire (so all his bullets hit you without any pause) then he would have gotten kicked/banned.
In cases like that all can really do is report him through the use of the scoreboard as someone has mentioned in the comments section.
You should put those settings in the designed steam option for the game.
Right click on CS:GO -> properties. Select set launch options... and type your settings
Example: 
This will save your settings.
Best Answer
I tried this in at least 20 matches and disconnected immediately after the scoreboard showed up and the prizes where drawn. I never got banned.
So yes, it is safe to disconnect when the scoreboard is shown.