Who is "Gever Rash v'Oshek Dalim"?
Rashi: He is an ignoramus judge. He oppresses the poor in judgment, because he is not deliberate in judgment.
Malbim: Sometimes the officers do not overpower, rather, the poor overpower in their rebellion. The entire nation, one rules over his colleague. The Rashim, who have nothing, oppress the Dalim, who Nisdaldelu (descended) from their property via the rebellion.
What is the meaning of "Matar Sochef v'Ein Lachem"?
Rashi: He is like torrential rain that floods the field, and it does not make Peros. A Mishnah (Kesuvos 7:8) says 'Nistapechah Sadehu.' It says "Nischaf Abirecha" (Yirmeyah 46:15) - they were inundated, slipped and stumbled.
Malbim: When the poor overpower in their rebellion, this is like torrential rain. If rain comes via cleaving of clouds, the water floods everything, to the point that there is no food. Instead of rain bringing food, it floods everything. So a flood of Rashim floods everything. We find this metaphor in Iyov 13.