The Sack Race is the fourth stage of Autumn = Sports Day!.
The battle begins with some Doges. After a few seconds in, 4 Pigge Backs will spawn, one after another followed by a few Doges. A few Pigge Backs will spawn again with a steady flow of Doges.
This stage is very easy. Take along anti-Reds if you need or rushers like Cow and Crazed Cow.