The question is, ‘is field based agility testing a true measure of agility?’ and the answer is no.
You can’t really say that the Illinois agility test or the T agility test are reliable and valid in measuring an athletes agility and this is due to many factors.
Agility is defined as “an open skill with change in velocity or direction in response to a stimulus, it must involve a sprint speed, change of direction speed and reactive agility” (Sheppard et al. 2006). However, most tests for agility do not include all of these variables and do not include the quick, sharp, 180-360 degree turns needed to define agility.
We all know the Illinois test as the ‘gold standard’ test for agility but it only involves slight changes in direction and a sprint which can only be referred to as the acceleration and deceleration at the beginning and end of the test.
In football, for example, agility would need to be measured with and without a football as players perform changes of direction, sprints and reaction in both these conditions in order to accurately measure agility in footballers. But, as you can probably guess, there is very little research surrounding this area.
Sheppard and Young 2006 suggest that perceptual and decision making factors are also involved within agility and how can this be measured in a 15 second field test?
Ref: Issue with the concept and definition of agility, Sheppard and Young 2006. Ref: Agility literature review: Classifications, training and testing. Sheppard, M. Young, W. 2006. Journal of Sports Sciences.