There are always a number of reasons why male athletes feel insecure and a few more for female athletes.
The common reason have to do with performance and their particular motivations behind why they play the sport. In younger children it is most often the parents driving them and the child wanting to please the parent and coach. The child does something good and they immediately ask "did you see that" or they are told to do something and say "watch me I can do that". They are seeking approval all the time.
Teens through adults it is often tied to performance level. Sometimes it is underestimated by the players and sometimes overestimated. It is no surprise more boys than girls overestimate their abilities. Thus since boys think they are better than they are the insecurities are when they see that other players around them are better, when coaches continue to tell them they are doing something wrong, and they are not winning as often as they think they should. Where as girls see performance in their own eyes, but tend to value what they think others think of their performance. The coach, parents and other players weigh heavy on their insecurity than does their own opinion more times than not. Please note this are generalization and not true of every male and female athlete.
This is only the tip of the iceberg on players insecurity but I hope this helps begin the thought process on the question.
earning money driving playing sport showing affection cooking
Jealousy is the thing that makes you feel insecure.
sometimes
earning money driving cooking showing affection playing sports
Over weight people fill intimated when they are playing sport... because there are fit people looking and making fun of them
insecure
You boost her confidence! complement her all the time and make her feel good.
Because there insecure which means they usually don't feel good about themselves so they try to make others feel bad about them so the insecure person can feel better about his or herself
"He left the house unlocked, feeling insecure about the safety of his belongings."
because they feel insecure
People that show a lot of skin are usually insecure or nervous and feel if they can dress "flashy" they can hide the fact they are insecure.
Because they feel insecure.