In my own opinion both are important for success in sport. Being an athlete is a physical amd mental draining career, as you always have to be in perfect mental and physical condition.
To start with, having physical strength is important in it own way. Since, most sports use a lot of energy, therefore they require enough strength to do it. For example, track, people who do track exercise their leg muscles so that they can have the strength to run long miles without feeling tired. Another example are weightlifters. These set of athletes train their enter body to build up their strength to lift heavy weights. If an athlete lacks the physical strength to partake in a sport that they have chosen then they will be more prone to injuries.
Additionally, having mental strength is also important. Some of these sports take a toll on an individual’s mind. To have the fortitude to say I will do this takes a lot of mental strength. Since, most people give up due to the stress they feel and heavy burden they have on their shoulders. Some athletes retire early due to the stress and pressure they feel and get from the media.
Furthermore, having both mental and physical strength helps an athlete grow more. For example, Serena Williams. Serena is a tennis player that faced many trials in journey as a tennis player from having issues with the referee to many more; that did not stop her in her journey. It helped her grow and become the tennis sensation we all love and appreciate.
Therefore, if someone wants to be an athlete having physical strength is not the only attribute you should posses. You should endeavor to also have mental strength.