Preheat oven to 350°F. Grease and flour a 9-by-13- inch baking pan; set aside.
Combine cake ingredients in large bowl. Mix on low speed for 30 seconds; scrape sides of bowl. Beat on medium-high speed for 2 minutes. Spread batter in pan.
Bake until a toothpick inserted in center comes out clean, 32 to 35 minutes. Cool on a rack for 10 minutes. Turn cake out onto rack and cool completely.
Beat together cream cheese, butter, confectioners' sugar and vanilla until smooth and fluffy. Set aside 3 (1/4-cup) portions of frosting. Leave 1 white. Tint 1 with yellow food coloring and another with orange. Tint remaining frosting with green food coloring; spread evenly over cooled cake.
Spoon white frosting into a pastry bag fitted with a small, round tip. Spread yellow frosting over 1 "end zone" and orange frosting over other. Pipe yard lines and end zone lines on cake. Use remaining frosting to write names of teams in end zones.
Use frosting and 3 pretzels to construct each "goal post"; stick a goal post in each end zone. Arrange "players," "refs" and "ball."