בְּשׁוּב־אוֹיְבַ֥י אָח֑וֹר יִכָּשְׁל֥וּ וְ֝יֹאבְד֗וּ מִפָּנֶֽיךָ׃
Radak on Psalms
When my enemies turn back, They stumble and perish at Thy presence. – For all the Philistine armies fled and turned back, as it is written (1 Sam. 17:51): "And when the Philistines saw that their champion was dead they fled."