Charles Ellicott Commentary Psalms 9:3

"When mine enemies turn back, They stumble and perish at thy presence." — Psalms 9:3 (ASV)

When. —Literally, in the turning of my enemies back, which may be either when they turned, or because they turned, or possibly with both ideas combined. The older versions have when.Psalms 9:2–3 form one sentence: I will be glad and rejoice in thee ... when mine enemies are turned back, (when) they fall and perish at thy presence.

Fall. —Better, stumble through weakness. So the Septuagint, are weak.