Is it a problem if legs are in the shape of an x?

Knock knees?Maybe. Hard to know from your question what you actually mean. I think you may be referring to a condition called knock knees or genu valgum. This could make the legs look like an x as they touch at the knees and widen at hips and ankles. Severe knock knees can make walking and running difficult and painful, and can lead to other problems in hips, feet or back.