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 host is red, it mostly makes all red, mostly for me red bar is caused because of sbmm, matching me with east coast players, while I'm from another side of the globe, which is the reason for lots of red bars