I believe that a twin flame runner and a twin flame chaser are both in fact runners. They are both running away from themselves.
The classic "runner" runs from the other twin flame because they spark their true soul self into awareness which is the part of themselves they have believed to not be good enough. They run from their true selves because they associate their true self with rejection. They don't understand that in truth their pain is cause by their own SELF rejection.
The classic "chaser" twin flame often is running from facing their true self and their wounds by overly focussing on what the running is doing or not doing. The way to subconsciously distract themselves from their own wounds coming up (to do with rejection again when the twin flame runner runs) is to keep looking outwardly towards the runner. When the chaser feels rejected by the runner, they often take it personally which is just a projection of their own SELF rejection.
Twin flame runners and chasers are very similar in this sense but their running from self plays out in these slightly different ways. Both are afraid to look too deeply inwards and take responsibility for their own wholeness and emotional security. The runner is afraid of being rejected because he / she places too much emphasis on self worth being determined by others and the chaser is feeling rejected because they are also placing the emphasis on their self worth coming from outside of themselves.
The chaser is feeling rejected because often they place unrealistic expectations upon the chaser due to a lack of understanding of the runner's difficulties in expressing their true self and their emotions. The runner is feeling rejected because he / she often feels that the chaser is trying to change them, trying to control them as if they are incompetent themselves and they feel generally misunderstood. Often the chaser can blame and criticise the runner which makes them run further. It all comes down to a basic lack of understanding when twin flames believe they will love each other and express that love in the exact same ways.
Oftentimes (but not always), the runner is the masculine. This is because men are brought up in this world to repress and deny their emotions, which causes their heart to close and their intuition to shut down. Oftentimes the masculine twin flame becomes a runner because they haven't been taught how to process intense emotions, only bottle them up and deny them. Twin flame connections are FULL of intense emotions which are very confusing the masculine who has repressed his feelings for so long that he doesn't know how to make sense of them.
Oftentimes, the feminine is the chaser and believes he is just as competent as working with his emotions and living his life through emotions as she is. Problems arise when he cannot live up to those expectations and she begins to feel rejected.