Legal proceedings were launched against Estermann, who competed at the London 2012 Olympics in team and individual events, in 2017 in relation to allegations of cruelty against horses Castlefield Eclipse and Lord Pepsi, as reported by The Horse and Hound.  

Estermann wrote Castlefield Eclipse at London 2012, where he was part of the Switzerland team that finished fourth in the team event, before finishing 17^th in the individual event.

Estermann and Castlefield Eclipse competed together at the 2013 and 2015 European Championships, as well as the 2014 World Equestrian Games.

The Swiss rider competed with Lord Pepsi at the 2018 World Cup Finals and 2019 European Championships.

The investigation into animal cruelty allegations against Estermann started in March 2017, leading the rider to withdraw from that year’s European Championships.

Estermann did return to the international stage while the investigation was ongoing competing at the 2019 European Championships, where he rode Lord Pepsi.

In November 2019 it was reported that Estermann had been found guilty of violating the Animal Welfare Act by a Swiss court, a decision appealed by Estermann, who subsequently announced that he would no longer compete for his country with immediate effect.

When the Cantonal Court in Lucerne heard his appeal in January 2021, they found Estermann guilty of multiple counts of "wilful animal cruelty" against Castlefield Eclipse in April 2016, and against Lord Pepsi in 2015, although he was cleared of two incidents involving Lord Pepsi between 2014 and 2017.

The case was taken to the Swiss Federal Supreme Court, and in March 2022 Estermann’s appeal was "partially admitted", meaning the previous ruling by the Cantonal Court was ruled not to stand.

Estermann was again found guilty by the Lucerne Cantonal Court in December 2022, with the appeal period for the revised sentence expiring on January 13 2023.

The Swiss Equestrian Federation said that it had now declared the conviction of Estermann as "final" and had submitted an appeal for a provisional suspension against him as a matter of urgency.

 A decision on whether Estermann will receive a provisional suspension is expected in the next few weeks.