Core can be one of those areas very much neglected or the "6 pack" look is what people desire.....
Having a good solid inner core helps with many areas of athletic performance and every session should incorporate some sort or core specific exercise.
1) stability - moving in all planes of movements occurs in most sports so being able to keep your bort stable and performance skills/techniques can be vitally important
2) Efficiency - using your core efficiently has been shown to improve power efforts such as sprint cycling and rotational movements such shown in field Hockey
3) Power - as mentioned, being able to use your core effectively such as a slap shot
4) injury prevention - exercises like the squat use core muscles to allow the torso to keep an upright posture and keep the bar path in a straight line. With poor core, positions in a typical exercise such as the squat can be compromised. Additionally, a forward in rugby must have exceptional core to cope with the demands of a scrum and avoid any injuries from this collapsing