When you lob something, you throw it up very high. If you lob a baseball from the outfield to the pitcher, you hurl it in an arc that ends right where the pitcher can catch it.
If you propel an object in an arc, you lob it — a soldier might lob a missile at the enemy, and a protester might lob a rock at a crowd. Tennis players can lob a ball by hitting it up and over the net. Today the noun lob means a throw (or hit) that follows an arc, but in the 14th century a lob was a "lazy lout," and in the 16th century it was "a lumpish thing."