Flower Shield is a fairy-type move. All Grass-type Pokémon on the field receive a one-stage boost to their Defense stat thanks to Flower Shield, with the exception of those that are using a move like Fly or Dig that grants them semi-invulnerability. If there are no appropriate Grass-type Pokémon, Flower Shield is unsuccessful. It is very similar to the move Rototiller.
Have you ever seen this move before?