Punching Bag - Embedded Physics problem

I’ve got the following problem:

I have a ground fixed punch bag (attached to the floor using a solid base with a spring on top).

What is the minimum sensor setup in order to determine:

• the force of the punch in the bag
• acceleration of the punch
• the speed of the punches (for multiple punches)

Notes:

• no sensor must be attached on the person punching the bag, only on the bag
• bag is punched in a limited vertical area (distance between tip of the bag and punching area is constant R)

Justify the answer with:

• sensors (only sensors must be used, no webcam tracking gimmicks)
• calculations

I do need to mention that you know:

• the mass of the punch
• the mass of the bag
• acceleration of the bag (by using an accelerometer)
• any height can be measured

The big problem that I face when modeling the system is: what if the user throws a series of punches amplifying or decreasing the oscillation of the bag? How do you model the equations to measure the parameters of interest then?