A Johnson County teenager is jailed in what  sheriff’s officers say was a baseball bat attack on his father.  It happened at Venus.   The Johnson County Sheriff’s office says they found 53-year old Robert Ehrhardt on the floor with severe head trauma.   They arrested his 17-year old son Kenneth.   The elder Ehrhardt was flown to JPS Hospital in Fort Worth where he is in critical condition.  His son is held on 125-thousand dollar bond.