A lot to get into one logline, but I should’ve mentioned the soldier is injured.

Also, you absolutely don’t want to see the soldier being saved! It would be clear that he is manipulating and using the boys and that is where the suspense would come through. Not sure how to portray that in a logline however…

The killing and her coming under protection of Leon happen so close together in the film that they are almost within the same story beat, so that isn’t a huge issue. However, her coming under the protection of Leon doesn’t really relate to her plot-line as far, as this logline is concerned, because it raises questions like “why is she under his protection and not an uncle or orphanage?” so, maybe,  try something like:

“When a 12 year old girl comes home to see her family murdered, she hides out in a friendly neighbours apartment only to discover that he is a lethal hitman and tries to convince him to train her so she can get her revenge.”

It’s quite long and clunky but all the necessary beats are there. Hope this helps.

Is he playing basketball at all in those thirteen years — like grifting and conning Ala White Men Can’t Jump or playing amateur leagues?

Why does he drop out of high school — what is the inciting incident that causes this?

What changes his luck and offers him a chance at redemption (and this should really be the inciting incident, e.g. When a once-prodigious basketball player gets a chance at redemption as… 

We would need more information to do a detailed logline. So far, this is far too vague and ambiguous. Hope this helps.

Would he have a number, because the way your logline descries the (somewhat limited) action of the script, it seems like it will end in tragedy. This could be a chance to do an inspiring never-get-me-down type screenplay (think like Rocky meets Pursuit of Happiness) instead of something seemingly quite depressing. Just food for thought about what story you are wanting to tell, and “sell”.