Possible Clues:

• Football player with management skills?
• Front part of a hand tool, say ... and the last word of 17-, 23-, 38- and 50-Across?
• Part of a weapon that does the damage
• Functional bit, colloquially, and a hint to 17-, 28-, 35- and 44-Across
• Front part, as of a rifle
• Front part of a gun, say
• Dangerous part of a weapon
• Transport in German city centre in loudest part doing the work
• Device's functional part
• It's an essential part of the process — that's the firm conclusion