I saw replays, Antonini goes in clumsily, but I'm not sure from that angle if the contact he has with Messi is enough for Messi to fall like he did, or be that defenite of a foul, can see how it would be given as pk, but not 100% sure one. While Nesta dragging Busquets shirt forever is quite clear to me, even if we see that happen often in the box, that was blatant shirt pulling, and defenite pk for me.