2. you / not play / your best game. (yet) 3. i /buy / the tickets. (by the time of their arrival) 5. the coach / talk / to him. (yesterday) 7. according to legend, the ancient olympic games / to be founded / by heracles, the son of zeus. 8. i / participate / in two competitions. (since i began exercising)

2. You / not play / your best game. (yet) - You haven't play your best game yet.
3. I /buy / the tickets. (by the time of their arrival) - I had bought the tickets by the time of their arrival. 
5. The coach / talk / to him. (yesterday) -The coach talked to him yesterday.
7. According to legend, the ancient Olympic Games / to be founded / by Heracles, the son of Zeus.  - According to legend, the ancient Olympic Games were founded by Heracles, the son of Zeus. 
8. I / participate / in two competitions. (since I began exercising) - I have participated in two competitions since I began exercising.