This could be an important case for the 1st Amendment. Couple things to note here.
First, the use of CS gas in warfare has been banned but the US still uses it for 'riot control'. Source
Second, is the use of weapons like L-RADs and rubber ball grenades that can injury journalist and peaceful protesters these weapons could be described as excessive force.
I hope the protesters are successful with this lawsuit to set a precedent for law enforcement that these tactics are not ok with the American people or the US Constitution.