About Sentani Ryu

Sentani-Ryu Aikido provides a combination of practical and traditional martial arts training in Clinton, Massachusetts. We focus on providing a friendly, safe, respectful, and sincere environment to study and practice Aikido for students of all levels.

The dojo focuses on the training and exploration of Aikido as a martial art. Our practice emphasizes both traditional techniques (takedowns, throws, immobilizations, and positioning) well as the study of Aikido in a modern context and its relationship to other martial arts and styles.

We include both traditional practice as well as live application training at more senior levels, including basic striking, grappling, and groundwork.


Mark Hatfield (Chief Instructor)
Mark Hatfield (Sensei)
Mark Hatfield began learning aikido in 1990 at college. Following graduation, he moved to Japan, where he trained under one of the first generation of professional aikido instructors. After living and teaching in Australia for 11 years, where he ran several different dojos, Mark earned his 4th degree black belt (“dan”) ranking.

Mark returned to the United States with his family in 2011, and founded Sentani-ryu Aikido in order to pursue his own vision for the future of Aikido based upon his experiences abroad.

Kevin O'Brien (Assistant Instructor)
Kevin O'Brien
Kevin began training in Aikido in 2000, while living in western Massachusetts. He has trained throughout the New England area, with experience in both Aikido as well as a number of other martial arts. He holds the rank of shodan (1st degree black belt), awarded by Hatfield-sensei in 2016.

Kevin teaches both Aikido as well as fundamentals classes that focus on striking, fitness, and other martial concepts.