I don't understand exactly the meaning of "部長が自分のミス俺のせいにしゃがってさ" the whole sentence is: 今日もさ 部長が自分のミス俺のせいにしゃがってさ冗談じゃ ないよ お前 部下をかばってこそ 上司だろ おい!
the meaning in the text is: today, the head of my department tried to blame me for his screwup. “This is wrong!” I said. “A chief is a chief because he protects his subordinates!”
but I want to know the grammar points of the aforesaid sentence and if the meaning is correct or not.