Idiom Definition:
Your browser does not support the audio element.
"to be on the ball"  
    to be quick to understand
     to be quick to react to situations usually due to being prepared
     
Synonyms: 
active, alert, alive, attentive, awake, bright, competent, knowledgeable, intelligent, observant, perceptive, quick, ready, sharp, vigilant, vital, watchful, wise
 
 
  
    
  
    This baseball player is quick to assess the situation and reacts quickly by running to catch the ball.
    He
 is literally 
on the ball.
