It's Siem de Jong, not Seim. He's the older brother of Luuk de Jong and has one cap to his name, which was a post-world cup friendly in which 17 players were given debuts, so not exactly a regular at that level yet. He is however a regular in the Ajax side that will be crowned champions tonight for the second time in a row (barring a miracle). Plays as an attacking midfielder, but has also played as a forward for Ajax sometimes. From what I've seen (and I usually avoid seeing Ajax play such is my dislike for them) he is decent, but not at the level his younger brother is at.