In short, to add a player:
Enter his name in A5
Select AC2, copy/paste formula in AD2, change one part of formula (in AD2): $B$4:$M$4 >> $B$5:$M$5, confirm formula with ctrl+shift+enter instead of simply enter.
Drag formula in AD2 down to AD21
For (simplest) datavalidation in B5:M5: select B5:M5 >> add datavalidation >>list >>Refers To:select AD2:AD21
The datavalidation in my example involves dynamic named ranges, which is more complicated but not essential.