The Hall of Fame Canadian hurler told a blogger in 2013 “ Willie McCovey was the most dangerous hitter I ever faced. He could turn on a pitch really quickly and make you look bad.”
http://baseballwithmatt.blogspot.com/2013/04/an-interview-with-hall-of-famer-fergie.html

The Hall of Famer and seven-time All-Star said he could handle most of the toughest hitters if he was throwing well. “But if I was a little off … Ernie Banks, Duke Snider. Henry Aaron and Willie Mays were marvelous.”
http://www.tuffstuff.com/news/baseball/pitcher_collector_extraordinaire_robin_roberts

Smith, who held the career saves record for 13 seasons, named Dawson the toughest hitter he ever faced during a 2004 interview with Boston.com.
http://archive.boston.com/sports/baseball/redsox/articles/2004/06/19/close_up_with_the_ultimate_closer/

In a 2002 book, Baylor was reported as calling the eight-time NBA champion “the toughest defender” he “ever went against.” Baylor explained that his fellow Hall of Famer was “very aggressive and totally unselfish.”
https://books.google.com/books?id=VeUfsWvUgesC&pg=PA122&lpg=PA122&dq=%22hal+greer%22+toughest+defender&source=bl&ots=WHrnPDboH1&sig=jTiTjuad9phGpDVPntlU8ioU1eY&hl=en&sa=X&ved=0ahUKEwjBxZuyprTRAhXFZCYKHRaWDDcQ6AEIGjAA#v=onepage&q=baylor%20sanders%20toughest%20defender&f=false

In a 2014 interview with SneakerReporter, the six-time All-Star said that, “without a doubt,” the toughest players to guard in his career were “Karl Malone and Scottie Pippen or Bernard King.” He emphasized the age difference between himself and King.
http://sneakerreporter.com/1-on-1-interview-with-nba-legend-reebok-ambassador-shawn-kemp/

The two-time MVP, seven-time All-Star and four-time Silver Slugger said of the Astros pitcher: “First of all he was about 6’8” Maybe even taller. [He] threw in the high 90s. Fastball, slider, and his control wasn’t the best so it always made things a little interesting.”
http://9inningknowitall.com/2013/01/12/5-good-questions-with-norm-dale-murphy/
https://reddit.com/r/IAmA/comments/158o2d/comment/c7k85fs

In an interview for the Montreal Canadiens website, Rock Raines said of his former White Sox teammate, “He was a slow-throwing lefthander who threw a cut fastball, and he always threw it in on my hands as a lefthanded hitter. Whenever I looked for his fastball, it would cut in on my hands, and when I moved off the plate to hit the cutter, he’d throw me a curveball. He was the only pitcher who I can say was really tough on me.” Raines, however, only had four career plate appearances against McCaskill.

http://canadiens.ice.nhl.com/club/page.htm?id=52644

The six-time All-Star gave the nod to the seven foot tall German in an article for The Players' Tribune in 2016. He wrote “That one-legged fadeaway? There’s just no stopping it.”
http://www.theplayerstribune.com/amare-stoudemire-knicks-suns-israel/

Mullin named the Bulls duo on the verge of his Hall of Fame induction. He said “They could smother you. Those two I didn’t really play against them a lot playing [in Golden State]. In Indiana – I wish I would have been a little younger, but those two were the toughest.”
http://www.csnbayarea.com/blog/matt-steinmetz/steinmetz-chris-mullins-all-time-list

Murphy, who, at 5'9", is the shortest NBA All-Star and Basketball Hall of Famer, told a journalist with the Lawrence World-Journal that West was the toughest defender he played against in his career. He explained that West had the “quickest hands” he ever saw.
http://www2.ljworld.com/news/2008/jul/13/keegan_best_starting_five_ever/