We are given the following information
Initial velocity of ball = 26 m/s
Distance traveled by ball = 9 cm = 9/100 = 0.09 m
We are asked to find the deceleration of the ball.
Recall the third equation of the motion given by

Where a is the deceleration, s is the distance traveled, vi is the initial velocity and vf is the final velocity of the ball.
vf = 0 since the ball is stopped after getting caught by the catcher.
Let us substitute the given values into the above equation

Therefore, the deceleration of the ball is -3755.56 m/s^2
The negative sign indicates deceleration.