That website looks suspicious. Arsenal played at home (Estadio Julio H. Grondona) against Colon and two days ago against San Lorenzo in the Copa Sudamericana. There is no reason that they would close it because it was constructed/ renovated in 2004. Arsenal is a tiny neighborhood club that has become a top flight team. Sort of like the Wimbledon or Watford (in the 80s) of BA.

http://www.sanlorenzo.com.ar/sudamericana2007_ficha.php

It's a small stadium, holding 16 or 18 thousand depending on the source. I have no idea if Boca fans will snap up the tickets. Your only option is probably to buy tickets at the box office.

http://www.celesteyrojo.com.ar/

Soccernet.com is reporting attendance for games so keep an eye on what happens when Arsenal play at home to other big BA clubs (Velez, River and San Lorenzo). The cup game against San Lorenzo appeared to be well attended from the video.

Arsenal has very little support. Only 2000 spectators against Colon.

I would take a cab to any stadium in BA.

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I would go to Racing vs. Independiente. That's a fantastic derby if you can get tickets.

I have not been to River's ground but it does have a running track, which I hate. It's the largest but hardly the best ground to watch football in BA.

Racing has an impressive bowl-like ground without a running track that holds 50 odd thousand.