Dennis Geiger is a local boy. He was born in Mosbach and started his footballing journey at nearby SV Sattelbach, before joining TSG's U12s in summer 2009. He grew into a leading role as a midfielder even at U15 level and captained the side to the South-German Championship in 2013. Geiger has also played for Germany's youth teams at every level since being called into the U15 side and was a runner-up with Germany's U17s at the European Championship in Bulgaria in May 2015. He missed the U17 World Cup in Chile in the same year due to injury. In early 2016, he played a big part in helping Hoffenheim's U19s reach the final of the German Championship, but couldn't prevent a 5-3 defeat to Borussia Dortmund. has become a regular for TSG in 2017/18. After making his debut in the DFB Pokal, he has gone on to play in the Bundesliga and the Champions League play-offs against Liverpool and was involved for most of the Europa League group stage campaign as well. He scored his first Bundesliga goal for Hoffenheim against Schalke on Matchday 6. To start 2018 he prolonged his existing contract with TSG until 2022.