Hacky Sack          
noun US trademark (also hacky sack, hacky-sack, hackey-sack) uk/ˈhæk.i ˌsæk/ us/ˈhæk.i ˌsæk/
 [ C ]沙包球,毽球,足沙包(Hacky Sack 本来是这种球的一个牌名称,后用来泛指这种球或体育活动) 
the brand name for a small soft ball that is often kicked in the air in games
  The two teenagers were kicking around a Hacky Sack in the school parking lot. 两名少年在学校停车场踢沙包球玩。 
 Footbag is the cool name for keeping a hacky sack in the air. “脚袋”是一个很酷的名字,指的是高高飞到空中的毽球。 
  [ U ]沙包球,毽球,足沙包 
a game played with a small soft ball
  Young people played Hacky Sack on the beach.  年轻人在沙滩上玩毽球。 
 It's an old Chinese sport and looks like a cross between badminton and hacky sack. 这种来自中国的活动历史悠久,看起来就像是羽毛球和沙包球的结合体。 
 - More examples
- I was juggling that thing like a hacky sack.
- The teacher tried giving boys hacky sacks to help them release energy and stimulate thinking.
- Combining the skills of volleyball, football, gymnastics and hacky sack might seem difficult to most of us.