Chordal Graphs and maximum independent sets
There are arbitrarily long sub-path whose induced subgraph contains no three independent vertices.  See the graph below for length 4:



Indeed, vertices in a sub-path induces an interval subgraph.  So you can use standard interval models (the endpoints of the interval for a vertex $v$ are the indices of leftmost and rightmost bags that contain $v$) to construct the tight example easily.  The graph given above have intervals:
[1,1], [1,2], [1,3], [2,4], [3,4],[4,4].  Likewise, you can construct for a subpath of length n: the basic idea is that each interval either starts from 1 or ends at n.