My experience is that 99/100 matches there is at least one red bar player.
Also from my experience i can say that one of those red bars is the host.
And the host has red bar, because everybody is playing on his connection.
Probably he has a very good ping, but too poor bandwidth for all players to play on. That's why red bars are mostly MVP's- they are hosting, so nr. 1 connection which counts.
This is the reason that after 2 years there are still red bars, every match......Bungie won't ban them, because they know it's P2P's matchmaking-system's fault.
Everybody knows that when you have very bad internet (red bar), you can't make a kill. Have tried it myself.
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I've lived out in the country with satellite internet and can assure you that red bars aren't hosts unless I was the host of every pvp match I've had since destiny released. I've moved now and haven't had a red bar since. It's just bad internet. I've hosted games with that satellite internet with 800+ ping and I was the green bar while everyone that connected to me was red.