You know that your output will have a different number of lines than your input, so you need to deal with the step of turning one input line into multiple output lines.

sub read_file {
  @lines = <>;
  chomp(@lines);
  for $line (@lines) {
    print join "\n", split ',', $line;
    print "\n"
  }
}
read_file;
[download]

$: perl 1158919.pl < Arsenal
Cech
Bellerin
Per
Koscielny
Nacho
Ramsey
Coquelin
Alexis
Ozil
Welbeck
Giroud
$:
[download]