Make a count from a dropdown category

Hi! I'm currently making a small tool with excel that will help me with my work in healthcare. I'm nowhere near an expert in excel but I know my way around specifying formulas. I'll have to keep some stuff vague to protect privacy, but I can clarify in the comments if needed.

In my work, some clients have incidents, but with those incidents sometimes other clients are involved (think of client A punching client B, where client A is the instigator). So far I have put all the clients in a drop down menu to ease the process for the ones that need to report the incidents (to prevent issues with capital letters, spacing etc.)

I want to make a count table (and from that count table a pie graph) of the clients who are involved with the incident. So a count table of client B, C and D, but only when the condition is met that its an incident filed under client A. I've looked at both a pivot table and the COUNTIF formula, but I can't get it to work. Do people got a good way to approach this?