Reading the ISFP description at personalitypage, I see nothing that corresponds with this for INFP:
"INFPs are flexible and laid-back, until one of their values is violated. In the face of their value system being threatened, INFPs can become aggressive defenders, fighting passionately for their cause." http://www.personalitypage.com/INFP.html
But the normally peaceful, laid-back ISFP can, disconcertingly, become just as passionate about some cause, although it's not a political or "higher value" cause.
Both INFP and ISFP have this aggressive "mama bear" side to their personalities with regard to some cause, although the ISFP cause would be more specific to the needs of those in their home than an INFP cause which would be more generally humanistic.