Create separate table/subquery to properly handle pickoffs

[droher]

Nuances to handle:

• Pickoffs should be credited to one and only one of the pitcher/catcher (as opposed to SB/CS), which requires correlating assist/putout data on the play
• Rare/erroneous/missing details: pitcher unassisted, no fielding credit, or non-pitcher-catcher getting first assist (likely erroneous or P/C implied in pitch sequence). Can find with rg -e "PO\d\([3-8]"
• Notify Retrosheet of box score generation error: https://www.baseball-reference.com/boxes/SEA/SEA201107170.shtml ("Pickoffs: Blake Beavan (0; Adrian Beltre, 2nd base)")