Field Hockey Ball Tracker I'm brand new to development and planning a project with my daughter to track speed and time in motion of a ball. 

Example, ball is at rest. It is then put into play, timer starts, and speed is tracked until ball is at rest. Is is possible to get accurate data with relatively inexpensive sensors? 

Data would look like: 
Moved 19 consecutive seconds, average speed during that time=33mph. 

Direction, elevation, acceleration changes, etc. would be ignored at this time. To start we just want average speed over time in use. We're having a bit of trouble deciding between accelerometers vs gyro vs magnetometer (or combination) 

Any assistance (even links to where to learn) would be greatly appreciated
An accelerometer is the way to go. There will be a fair amount of math to go thru in order  to convert the acceleration value into speed. I can't explain it better than this answer.

An gyro would give you the angular rate on the ball and the magnetometer could give you the ball orientation relative to the magnetic north.