@Scratchlaxin r/Sprinting • Recommends
On “Basketball to Sprinting (15.29 100m)”
The biggest form issue is that when your arms are swinging back, you aren't keeping them at 90 degrees. Right angles are good!
If you want a set of drills that teach this stuff: link to this video
Watch the video form carefully.
5 seconds of drill, 1 minute of rest. 10 total drills, then two all out sprints to put it together. Do it 3 times a week. You'll likely get to around a 14s 100m fairly quickly.