Complex sentence: In knitting, each stitch is supported by the corresponding stitch in the row above and it supports the corresponding stitch in the row below, whereas crochet stitches are only supported by and support the stitches on either side of it.
Split into simpler sentences: In knitting, each stitch is supported by the corresponding stitch in the row above and it supports the corresponding stitch in the row below. In crochet each stitch is only supported by and supports the stitches on either side of it.