Fitness Roundup: 12 Strength and Circuit Workouts including this total body stability ball workout from running It works and you can do this once a week
5 minute plank workout per day. Plank workout for Abs, Chest, Butt, Back & Core. Planking exercise for beginners.
450 rep Abs on Fire Medicine Ball Workout - Looking for a challenging Abs Workout?
Total Abs Workout 2014 - Not sure which exercise targets which muscle? Here's a nice visual guide to help put together a workout that targets your abs and obliques.
The 30 minute Glute-building body weight workout
Hiit The Stairs Full Body Hiit Workout Transform Yourself Amp Your Life Get Fit Amp Healthy Start Yo
Stair/Stadium Bodyweight Bootcamp Workout -- This looks way more reasonable than a lot of circuit workouts, and more adaptable to having stairs but not a field, and vice versa.