User blog comment:B214/High School DxD New Episode 3 Discussion/@comment-16075832-20130723034745/@comment-1359322-20130723090246

First, Issei losing to Irina is canon, the part where he lost to Sona isn't, that was Anime only. In the original story, Sona and her team appear after Issei defeats Riser. The dogdeball and tennis game were part of their school events, into for the Anime to fit in 12 Episodes they introduce Sona and her team earlier and add in the dodgeball and tennis game that was supposed to be on the school event.

Second, High School DxD is a Light Novel that was adapted into a Manga and later an Anime. So the original version of DxD is from the LN, the anime mix in some of the side stories written by Ishibumi as well as increasing the Fanservice. Also the LN is still continuing.