The acceleration of the ball is -9.8 meter per sec square acting as deceleration when the ball left the hand after being thrown upwards.
Explanation:
The ball is thrown with a speed of 14 m/s and the moment it comes into the projectile, gravity starts to work on it. The gravity applies the uniform acceleration of 9.8 m/s^2.
This acceleration is in the form of deceleration [the negative acceleration] is termed as the deceleration. And here, the ball is thrown opposite to the gravity and hence the motion is against the gravity, the acceleration becomes -9.8 m/s^2.