It’s probably a mix of AF tracking limits and a little too little margin for error, not just one mistake.

For fast action, AF-C helps, but no autofocus system gets every frame perfectly sharp. Tracking performance depends on the camera, lens, AF mode, and how well the AF point stays on the subject. Using only a single center point can make this harder if the subject moves off that point during the burst. A zone/dynamic-area AF mode often improves keeper rate for action.

Depth of field is another factor. At 18mm, stopping down slightly from f/3.5 to f/4 can give you noticeably more depth of field, which makes small focus errors less visible. You can raise ISO to maintain shutter speed.

Also separate blur from missed focus: if shutter speed is marginal, motion blur can look like poor focus. The polarizer may have reduced available light, forcing the camera toward wider apertures or slower shutter speeds.

In short: use a faster shutter if needed, stop down a bit for more depth of field, consider zone/dynamic AF instead of a single point, and expect that action shooting will never have a 100% keeper rate.