Best way to inspire competitiveness

I have a 12u team of all good kids. Most are ok fundamentally and continue to get better. The one area they struggle in is in being competitive. In 5 years they’ve seldom been successful but mostly because they never seem to be able to push themselves in a game situation. They look good in bp then I the game they half swing or hope for a walk. I can’t seem to get that one kid that will spark the rest and inspire the “refuse to lose” mentality. We’ve done competitive practices and so forth and they do well with those but when they take the field it’s like they’re beat before the cross the lines! In my mind I know they really just need to experience success but I don’t now how to get them there without some competitive spirit on their part. Somebody help!