וַיִּצְעֲק֥וּ בְנֵֽי־יִשְׂרָאֵ֖ל אֶל־יְהוָ֑ה כִּ֠י תְּשַׁ֨ע מֵא֤וֹת רֶֽכֶב־בַּרְזֶל֙ ל֔וֹ וְ֠הוּא לָחַ֞ץ אֶת־בְּנֵ֧י יִשְׂרָאֵ֛ל בְּחָזְקָ֖ה עֶשְׂרִ֥ים שָׁנָֽה׃ (ס)
И возопили сыны Израилевы к Господу; у него было девятьсот железных колесниц; и двадцать лет он сильно угнетал сынов Израилевых.
Rashi on Judges
Oppressed the Bnei Yisroel intensely. R' Tanchuma expounded, through ridicule. Similarly, it is said, "Your remarks offend me intensely."2Malachi, 3:13. Vs. 14, 15 there define the offensive remarks as ridicule of the worship of Adonoy.
Metzudat David on Judges
it was because of the nine hundred chariots that they did not have the feeling of approaching them in battle stirring in their hears. they therefore cried out to Hashem in prayer