my $score = 'score SOME_WORD 3.0 3.0 3.0 3.0';
my $removed_word = $score =~ s/^(score\s\b\w+\b\s)//;

# $removed_word now contains 'score' plus whatever 
# unknown word you removed, plus trailing single space.
# $score now is left only with what comes after the removed word,
# and preceding whitespace has been removed.

# Now you can do whatever processing you wish.

# Then to put it back together:

$string = $removed_word . $score;