I'll go on the record agreeing with the penalty call. Even after viewing the replay. Why? Costa did step on the sliding defender, but not deliberately to draw a penalty IMO. He did it because he had to plant his foot somewhere, and the defender's careless slide meant that defender was right underneath where Costa was naturally about to plant his foot--and when the defender's slide continued, it took that foot right out from under the attacker. Go back to the clip... watch Costa's eyes. He's made a little move to avoid the defender and is looking to plant and go towards goal, not looking down to step on the defender. IMHO Costa did not "initiate" the contact in the way many here seem to think.
Not mentioned or noticed is the pull-down before the 5:1 If one watches the replay of the 5th goal one can see that Pique pulls down Lens in the build up. Even though it was still a goal, it should have been a clear yellow.
The inference from above comment is that Costa has the unequivocal right to the piece of ground that at the moment was occupied by the defender's leg, right? I don't buy it. Whether an intentional act or not by Costa, if there was not contact by defender to attacker and the attacker ended up stepping on the defender's leg, I have a foul coming out. Regardless I agree with those that hold the position that the defender put himself in a very precarious position by sliding in such a manner. Personally, during the live transmission, I thought that the defender actually hooked Costa's foot/ankle with the slide and which ultimately caused Costa to end up on the ground. Thus I agreed with the penalty call. With the benefit of replay (slo mo at that), I can't agree with the call.
Well, if the defender is underneath where Costa's leg was originally--like it looks to me--, yes. A player has a right to the space they are occupying. Players will usually do their best to jump and avoid such contact, but if that sliding player is still under you when you come down naturally, I can't see that as a foul on the jumping attacker. The defender needs to be more careful about where he slides. He put himself into the space that Costa was occupying, and only missed clattering him right off was that Costa had jumped up a bit to pivot. I agree that live, I thought the defender hooked Costa's foot as well. But IMO the effect of the slide took the foot out in pretty much the same way, with the same result--a foul on the defender and penalty in my book.
I understand and am fully aware of this part of the laws of the game. We will have to agree to disagree based on the complete book of information available to us post-game. Based on the video in post #176, I think the defender has the same right to the piece of turf as Costa based on the location of Costa's body and his landing zone.