Who are "Yasom va'Dach"?
Rashi: They are Yisrael, who are orphans and Dachim (crushed).
Radak: Orphans and downtrodden people.
Why does the verse teach about judging "Yasom va'Dach"?
Radak: This is the (Malbim - one) prayer of the humble, that Hashem judge their case against their oppressors.
What is the meaning of "Bal Yosif Od La'arotz Enosh"?
Rashi: Esav (some texts - Amalek) should not continue to crush and break the seriously ill.
Radak: The orphans and downtrodden will not fear people, [only You]. La'arotz is Po'el Yotzei (to make others fear), like "La'arotz ha'Aretz"(Yeshayah 2:19), "heAleh Nidaf Ta'arotz" (Iyov 13:25).
Malbim: This is the second prayer of the humble, that no longer will a tyrant rule and conquer the land. Rather, Hashem will do Mishpat, and all will recognize his Hashgachah.