If it were a ligament sprain could you explain why you think the pain may randomly come and go over very short periods of time (eg there one minute, gone the next, there again the next)? I would have thought that a ligament or tendon sprain would mean pretty much constant pain that may subside after rest but come back as soon as activity is resumed, and likely get worse with prolonged activity.

Fwiw I've had this pain for about 2 weeks or so. On the day I posted this thread I started doing SMR on my calves and around my ankle, and doing ankle mobility drills. I have not reduced my sporting activity at all, yet the pain seems to have started to disappear. To me this would suggest that something in either calf or around my ankle is tight or stiff resulting in excessive tension through the plantar fascia and causing pain at the area where the pf connects to the metatarsal joint. Would this make sense?