I typed the command in a command block:
say @p(team=SpleefP1,score_SpleefDeaths_min=1) lost the Spleef Game!

I used brackets, but this text editor turns everything encased in brackets into a link, so I used parentheses so that it wouldn't do that.

When I gave power to the command block, it said:
(and robblie_bob lost the Spleef Game!) "robblie_bob is my username"

To my knowledge, there is not supposed to be an "and" in front of the
username.