Some people are saying they had to do all of these with 1 character however i did not and neither did some other people. so if your achievement doesn't pop try doing them all for 1 character or to be safe begin by doing them all with the same character.
This is quite a simple achievement once you actually know what you need. To comlete this achievement all you need to do i WIN each of the following (one event of each).
Gold on any 1 Triathlon
Gold on any 1 Moto/ATV Off-Road Race
Gold on any 1 Water Race
Gold on any 1 Flight School Lesson (has to be the Los Santos INternational airport not sandy shores)
Gold on any 1 challenge on 1 gun at the Gun Range.
Gold on any 1 street race
If you leave the street race Franklin has to complete one as a strangers and freaks mission. however this mission only appears from 22:00 to 5:00. Once again you dont need to get the gold medal only need to come first.
No need to get Gold on all, example, Triathlons, just 1 is enough :)
You don't need Tennis, Golf, Darts and stuff.
If any appear on your map and then disappear and you cannot find them try saving then reloading the save. However this will not work if they have not shown up yet. This is because some events don't appear till certain progress through the campaing.