Validating CSV Rows

Validate every row before storing it.

if (count($row) !== 4) {
    $rowErrors[] = "Row $rowNumber has the wrong number of fields.";
    continue;
}

[$matchId, $teamName, $winsRaw, $lossesRaw] = array_map("trim", $row);

$wins = filter_var($winsRaw, FILTER_VALIDATE_INT);
$losses = filter_var($lossesRaw, FILTER_VALIDATE_INT);

if ($matchId === "" || $teamName === "") {
    $rowErrors[] = "Row $rowNumber has a missing required value.";
    continue;
}
if ($wins === false || $losses === false || $wins < 0 || $losses < 0) {
    $rowErrors[] = "Row $rowNumber has invalid results.";
    continue;
}

The loop is iteration; each validation decision is selection. Preserve row numbers so an administrator can correct the source.

Define whether one bad row rejects the whole file or only that row. For assessed work, justify the policy from integrity and user needs.

Check

Test blank, extra, missing, non-numeric, negative and duplicate values.