#1 - Side view of player in the ready-to-react neutral position just as the ball is coming off his opponent's racket.  His grip is an EASTERN FH so no grip change is necessary.
#2 - Player sees that the ball is coming to his FH and initiates the pivot with left hand remaining on the racket.  Weight starts to transfer to the right foot.  Right elbow leads back slightly which will enhance the racket head speed of the swing.
#3 - Weight has almost entirely transferred to right foot with the left foot just starting to step in toward the anticipated path of the ball.  Left hand releases the racket and shoulders are turned squarely.
#4 - I have added a broken arrow to illustrate the future path of the racket head which is the classic loop motion.  This motion if generated from picture #2 or #3 will provide the player with an almost effortless swing.  Please make note of the nice hitting base establish by the step to the left foot.  The majority of the player's weight is still on the back right foot, thus staying with the flow of the racket.
#5 - The weight transfer has started as the racket head drop down in the loop motion.  Player is clearly locked onto the ball with his eyes.  Left hand continues to separate away from right.  Nice hitting base!
The racket  head has clearly dropped to a position below the ball.  This will produce topspin at contact.
#6 - The racket head has been highlighted in GREEN to emphasize its location below the ball thus assuring a bit of topspin.  Weight has come onto the left foot with distance between arms closing.