I don't personally feel like this incident - terrible as it is - merits criminal charges, but I'm also not going to pretend I'm particularly familiar with how the UK legal system works in these instances. From my perspective, the player could have made a safer move, but I don't think a split second miscalculation like that rises to the level of manslaughter. It was simply a horrible accident. If a thorough investigation determines his actions to be criminal by UK standards, though, I guess there's not much that can be said to refute it. I guess it boils down to whether intentionally kicking his leg out is criminally reckless - a gray area.