To those speculating as to why he would have been asked to cross his ankles, this is standard arrest protocol in a high-risk scenario. If a subject is lying prone or kneeling with their ankles crossed, the un-crossing of ankles requires an additional movement prior to any effort to escape or physically confront arresting officers. This provides officers more reaction time.
But asking a subject to crawl forward with crossed ankles is not a standard safe arrest practice or protocol.
None of the arrest and search training documentation I have seen online advocates instructing a subject to crawl at all.
Is asking someone to crawl with crossed ankles a standard arrest practice in the United States?