I loathed sports day in primary school, it was horrible being forced from a young age to do things I was crap at publicly. PE was also a boring nightmare repeatedly doing rounders and other games letting the whole team down. It really put me off sport.
Secondary school sports day was much better. You basically got to spend the day milling round in the sunshine with friends (we weren't made to sit with our class), and they had lots more individual type events like javelin where you went one at a time and got points based on how far it went, rather than being directly pitted against one another. They also emphasised you didn't have to do anything, but got one house point for every event you participated in - so me and unsporty friends would wander along to events and have a go and contribute a few points to our houses by the end of the day.
PE lessons also got better by year 10 when we could choose what we did to some extent, but I still hated sport/PE.
Yet by the age of 20, much to everyone's surprise, I was at outdoor college, regularly walking in the hills, climbing, kayaking, etc. Turns out I didn't hate all physical exercise, just PE lessons and the way it was taught at school. (I always known exercise was necessarily and was self conscious of my weight so walked everywhere but had seen it as a necessary evil!)
Now 20 years since those sports days, I am slim and fit, exercising regularly and eating well. It's not school sports days that will help people have a healthy attitude to exercise - they put me off for a long time.