"Everyday interactions we have with other people are definitely contagious, in terms of happiness," says Nicholas Christakis, a professor at Harvard Medical School and an author of the study.
According to this article, "the study is impressive in showing that moods can be contagious."
For those who've been in a locker room and have seen how one player's bad mood can negatively affect a team, these findings aren't particularly surprising.
The good news is, as coaches have sensed for a long time, having players on your roster who are "good guys" -- people who are optimistic with good attitudes (i.e., "happy") -- are likely to have a genuine impact on your team.