We are given the following information:
Mass of ball = 145 g = 0.145 kg
Mass of player = 65 kg
Initial velocity of ball = 100 mph
Let us first convert 100 mph into cm/s
1 mph is equal to 44.704 cm/s

The initial momentum is given by
![\begin{gathered} p_1=m_1\cdot u_1+m_2\cdot u_1 \\ p_1=0.145\cdot4470.4+65\cdot0 \\ p_1=648.21\: \frac{\operatorname{kg}\cdot cm}{s} \end{gathered}]()
The final momentum is given by

The total momentum of the system must be conserved so,

Therefore, the player acquires a speed of 9.9 cm/s after catching the ball.