Hotspot on ball of foot
 

Currently riding with a pair of Pearl Izumi mtb shoes I picked up at the beginning of last summer and a set of Shimano spds I've been riding for years. I've encountered no problems or soreness whatsoever since I started riding this set up until the past few days. A pretty bad hot spot has developed under the ball of my left foot, just underneath my big toe. I've checked out the pedals and cleats and nothing seems to have shifted, loosened or changed in any way. I did just switch out my seatpost/saddle so I'm guessing tinkering with the height and fore/aft position is the culprit, but then why only my left foot? Any suggestions are greatly appreciated. my foot is sore...

Do a search for past threads on this subject. The problem is usually related to the small surface area of your pedals putting pressure on your foot. You might want to switch to a combination pedal where the spd is surrounded by a platform pedal. Other causes could be a bad fit of your shoe - too tight or sock bunched slightly, poor insoles, etc.

Morton's Neuroma? I'm not a podiatrist but I like playing one on the internet...

My Rx is to get some custom insoles...

which insurance company shall i bill? :)

How many miles since you tinkered with the seat post? I'd say if it is less than 100 miles, there could be some adaptation still happening.

If it persists, I'd see either a fitter that can deal with your fit and foot position. If you've been using these shoes for a long time without incident, I feel like you'd just be chasing your tail in going that route or for custom insoles/orthotics. Also, perhaps refocus on your pedal stroke? I tend to get that hot spot feeling when I'm pushing down on the pedals. When I focus a bit more on pedaling circles, it helps alleviate it.

That is my 2 cents.