Casey Candaele
... that Helen Callaghan of the AAGPBL and son Casey Candaele are the only mother/son duo to play professional baseball, with Candaele having a career batting average seven points lower than his mother's?
... that <a href="./Helen_Callaghan" id="mwCSk" rel="mw:WikiLink" title="Helen Callaghan">Helen Callaghan</a> of the <a href="./All-American_Girls_Professional_Baseball_League" id="mwCSo" rel="mw:WikiLink" title="All-American Girls Professional Baseball League">AAGPBL</a> and son <b id="mwCSs"><a href="./Casey_Candaele" id="mwCSw" rel="mw:WikiLink" title="Casey Candaele">Casey Candaele</a></b> are the only mother/son duo to play professional baseball, with Candaele having a career <a href="./Batting_average" id="mwCS0" rel="mw:WikiLink" title="Batting average">batting average</a> seven points lower than his mother's?