Some people feel that the The victory in sports lies in thean individual's physical superiorability ofhas the individualgreatest influence on their success in sports; however, others feel that mental attitude is a more important factor toin winning games. Some people feel that an individual's physical ability has the greatest influence on their success in sports; however, others feel that mental attitude is a more important factor in winning games.

This sounds more natural to me - let me know if you have any questions.

In my opinion, the psychological conditiony plays a more important role in the case offor individuals with a high level of athleticism. In my opinion, psychology plays a more important role for individuals with a high level of athleticism.

Or "highly athletic individuals." Sometimes shorter is better :) "The psychological condition" would be like a particular state of mind - I think you mean people's psychology in general.

2. Dark horses and comeback winners are often those who possess a good mental condition. 2. Dark horses and comeback winners are often those who possess a good mental condition.

More concise: Dark horses and comeback winners tend to possess a good mental condition.

3. In sports competitions and training, there are many obstacles to be encountered. 3. In sports competitions and training, there are many obstacles to be encountered.

Better to avoid the passive voice: People encounter many obstacles in sports competitions and training.

Often it isthese are not a physical obstacles, but a mental ones. Often these are not physical obstacles, but mental ones.

Plural because you mentioned multiple obstacles in the previous sentence.