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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If the host is the red bar, then it is every other players fault that he is lagging. The game picks the host with the best network statistics eg nat type, and real time download/ upload speeds, and compares and picks the best one. If they are lagging, it is because their connection to other players that they are trying to brings together sucks, hence the name peer-to-peer connection.