[1] Born in Biel/Bienne, Bern, He made his senior debut for BSC Young Boys at the age of 17 years on 14 September 2008 in a 2–1 victory over AC Bellinzona, replacing Marc Schneider in the starting eleven due to suspension.

[2] Since that match, he was a regular starter for the club in their three-man defence, alongside Saif Ghezal and Miguel Alfredo Portillo.

[5] After an unsuccessful half year at Young Boys, he decided to transfer to Swiss side FC Luzern for an undisclosed fee.

[6] On 21 July 2017, Major League Soccer side San Jose Earthquakes announced it had signed Affolter to a multi-year contract on a free transfer from Luzern.

[7] He made his first appearance for San Jose on 9 August, starting in the U.S. Open Cup semifinal against Sporting Kansas City and substituting out during extra time in the 103rd minute.