use strict;
use warnings;

my %Participants;

while (<DATA>) {
    chomp;
    
    my ($name, $tail) = split / /, $_, 2;
    
    next if ! defined ($name) || exists $Participants{$name};
    $Participants{$name} = $tail;
    print "Added $name: $tail\n";
}

__DATA__
Fred Red team
Joe Blue Team
Pete Blue Team
Fred Red Team
Annie Red Team
Lee Green Team
Steve Green Team