The veteran forward, named among the substitutes by Killie boss Steve Clarke, was warming up on the touchline when TV cameras showed a missile striking Boyd on the arm as he warmed up in front of the visiting fans.
The former Scotland international appeared unhurt but Sky Sports pundits Kris Commons and James McFadden condemned the incident at half time, branding it “disgusting”.
“It’s unacceptable, Kris has got his opinions and if you want to give him stick that’s fine,” McFadden said.
“He’s a grown man, he likes to give it out and he can take it but to throw coins - there’s no place for it. Absolutely no place for it. It’s disgusting.”
Commons said: “This isn’t an isolated incident - this has happened at Livingston, St Mirren, Tynecastle... it needs stamped out very, very quickly.”
Sky Sports also reported that Boyd, who had two spells with Rangers earlier in his career, had been subjected to sectarian abuse from some sections of the support.
McFadden added: “This season, on the pitch, has been absolutely brilliant for Scottish football.
“And some of the behaviour of a minority of fans is trying to derail that, and spoil it. [There’s] absolutely no place for it.”
Former Hibs head coach Neil Lennon was struck by a coin thrown from the Hearts support during the Edinburgh derby on October 31, while Alfredo Morelos had missiles thrown at him during a Rangers-St Mirren match at the Simple Digital Arena. And at the Tony Macaroni Arena, an assistant referee required stitches after receiving a cut head after anobject was thrown at him during a Premiership clash between Livingston and Rangers.
Celtic won the match at Rugby Park 1-0, thanks to Scott Brown’s injury-time winner. The Hoops captain picked up a second yellow card and was sent off for excessive celebration while Timothy Weah was booked after the final whistle.
Kilmarnock defender Kirk Broadfoot was shown a straight red card during the match for a challenge on Brown with around 15 minutes remaining.