Churning This Quarter KPI for Sales Productivity

I want to see my sales team ranked by churn and then an easy way to see some of the biggest churn accounts within each salesperson.

"Churning This Quarter" will be defined as any account that spent this Quarter last year but is <= $0 this Quarter this year.

I'd also like to see "Potential Churn Next Quarter" where any account that spent next quarter last year but is <= $0 next quarter this year.