One 17-year-old nearly died, and was reanimated after the strike which hit the outdoor football pitch at around 3pm.
Police from Ingoldingen, Baden Württemberg, said two football teams of teenagers were warming up on the pitch as light drizzle started to fall.
When the lightning struck, three boys who were standing at the edge of the pitch near a metal fence, were seriously hurt.
One of them stopped breathing and was given the kiss of life by first aiders. He was taken by rescue helicopter to a hospital in Ulm.
Further players and onlookers, as well as two teenage girls who were raking the beach volley pitch nearby, were also injured.
The police spokesman said, “No-one could have expected what happened, as it had started to drizzle slightly, but there was no storm to be heard or seen in the sky.”