We try to expose my son, who recently turned 6, to as many sports as possible. If he chooses to sign up for a sport, he has to at least finish out the season. The only "sport" he has decided not to play anymore is karate, as it became boring to him. He still plays soccer, baseball, lacrosse, and hockey. This was his first year of organized hockey, and he did quite well and has been selected to be on the travel team next year. He loves it so I am supportive. I always make sure to tell him before every practice/game "I love you....have fun and do your personal best."
I have witnessed some pretty atrocious incidents at hockey practice this year. One Father in particular, who has one son that plays D-1 hockey and another on his way to prep-school to play hockey, is really hard on his youngest son to perform well. The poor kid is 8 years old, and he is not particularly coordinated or athletically gifted. He tries his best, but he is clearly not amongst the best players on his team. I have witnessed this Father verbally berating his son for playing poorly, and on several occasions has been mildly physically abusive (i.e., slap to the back of the head, kick in the butt). It really makes me feel sorry for this kid. No matter how hard he tries he will always be a "failure" in his Father's eyes based on what his siblings have accomplished.
Gug's you should check out the documentary Trophy Kids on Netflix. The parents are pretty over-the-top, but it is a good illustration of what you're talking about.