Excessive sharpness or edge enhancement can create halos around contrast boundaries. Compression can also cause ringing near edges. Compare the same scene with restrained picture processing, and inspect another source before deciding whether the outline was introduced locally or already exists in the video.
Choose a revealing boundary
A dark jacket against a bright wall, a scoreboard or a building against the sky makes halos easier to see. Avoid judging from a heavily stylised programme whose look may be intentional. Look at both sides of the edge and check whether the outline remains fixed as the object moves.
Reduce one control at a time
Start with sharpness, then any separately documented detail or edge-enhancement option. Keep contrast and colour stable so the comparison remains meaningful. If the outline disappears while real texture stays visible, the stronger setting was likely adding an artificial transition rather than useful source detail.
Know when to stop adjusting
If the halo remains in another supported player or on another display, it may be part of the encoded source. More local filtering can soften the entire picture without removing the cause. Record the programme and time for support and use a neutral baseline for normal viewing rather than compensating globally for one difficult source.