Jack Mercer vs. Sean O'Sullivan — Career Comparison

Sean O'Sullivan built a career as a starting pitcher and Jack Mercer as a reliever — different jobs with different demands — but on the metrics that apply to both, a comparison is still worth making. Jack Mercer posted stronger surface numbers — ERA 0 and WHIP 2.000 compared to 6.01 and 1.616 for Sean O'Sullivan. By the career numbers, Jack Mercer had the better of this cross-role comparison — though era context would sharpen the verdict.