Portable Circular Saw Safety Precautions
Be sure the switch actuates properly. It should turn the tool on and return to the off position after release.
Use sharp blades. Dull blades cause binding, stalling and possible kickback. They also waste power and reduce motor and switch life.
Use the correct blade for the application. Check this carefully. Does it have the proper size and shape arbor hole? Is the speed marked on the blade at least as high as the no-load RPM on the saw's nameplate?