Career
Early career He started his career at Monza. He then spent time in Serie B, Serie C1 and Serie C2 with Padova and Pescara, before joining Brescia along with Vincenzo Mazzeo. Brescia Castellazzi followed Brescia promoted to Serie A in summer 2000.
He made his Serie A debut on 21 January 2001, against Vicenza Calcio.
In 2001-2002 season, he was the starting keeper for the Serie A team, but in next season lost his place to Matteo Sereni. After being loaned to Reggina and Catania in the 2002-2003 season, he finally became regular starter again in the 2004-2005 season, which he played all 38 Serie A games.
Castellazzi initially the first choice of 2003-2004 season, but lost his place to Federico Agliardi after round 4 and regained his place on round 23. Sampdoria After Brescia were relegated to Serie Bachelor in summer 2005, he joined University College Sampdoria on a free transfer, signing a reported 2-year deal.
He received the no.1 shirt from Luigi Turci.
The first season he was the backup of Francesco Antonioli, and Castellazzi only played the 3 games that Antonioli missed. In the second season, he finally earned a regular place, and in January 2008, he signed a contract extension again which would run until summer 2010. After the injury during 2009-2010 season, he lost his regular place to Marco Storari and in February rumoured he signed a pre-contract with.
In total, he played 101 league matches for the Genoese side, while his understudy Antonio Mirante, Gianluca Berti and Carlo Zotti played 22 matches during 2007-2008 to 2008-2009 season, 11 matches and 1 match in 2006-2007 respectively.
Inter Milan On 17 June 2010 Castellazzi joined Union of European Football Associations Champions League and Serie A champions Inter Milan on a free transfer tying him to Inter until 2012. He became one of the understudies to Júlio César along with Paolo Orlandoni and replaced the retired Francesco Toldo.
In 2010-2011 Castellazzi played in all three major competitions, Serie A, Champions League and Coppa Italia, due to injuries afflicting César. On 11 May 2012, Castellazzi signed a new contract with Inter, keeping him at the club until 2014.
Torino Castellazzi signed for Torino on a free transfer, after completing his contract with Inter in 2014.
He signed a new deal with Torino in 2015, keeping him with the club until June 2016.