But, Ecofarm, the way I understand it, it's not the national scene that people are concerned about, but the local, state-wide competitions.
Since I have no proof of this, you can freely consider it to be anecdotal, but I saw a national news report during the past year or so that talked about a male athlete at a high school who became a transgendered female. To be fair to her new identity, the school let her join the female track team. She promptly beat all the other girls in every event, and it wasn't even close. In doing so, she broke every female record at the school. She moved on to the district competitions and easily won every event there, too. She went on to the state level and won everything there, as well.
It would be easy to cheer her on, but when you look at all the other girls who had practiced and worked all their lives toward winning those races and awards only to have their dreams shattered by someone who had trained as a boy and who was born with a muscular advantage--well, you can understand how it broke the hearts of many, many girls and their parents.
For that reason, I think that sports that require a certain amount of strength should be restricted to the gender of which one was born. All other sports should be open to everybody.