This would probably be the easiest since it is all bodyweight exercises, no equipment needed.
Bodyweight Circuit #3 along with Core Workout
25 Hindu Squats
15 High Pulls with resistence band
12 Pike Press or Dips
and go through the circuit 3-4 times. Follow it up with a core workout. An easy sample core workout could be...
3x25 Russian twists with weight in your hands
3X30 second plank holds
3x25 Leg Lifts
Do the whole workout (first circuit followed by core workout) 2-3 times a week with a day inbetween to recover.
As for the treadmill, I dont see a use for it. Sprinting is the best way to build anaerobic endurance, which is what you use for baseball. Mark off 30-40 yards, sprint and then walk back to the starting point. Repeat 10-12 times.